The Compromise of the Jpeg Format

As mentioned in the digital formats blog last week, each time you edit and save a jpeg file a process takes place that aims to reduce the size of the resulting file. This entails making some approximations about the content (the colour) of some pixels. Repeatedly saving a jpeg file will, therefore, degrade its quality.

Whenever you save a jpeg file, most programs will offer you a choice as to the trade-off you would like to make between the size and the quality of the file you are going to create. In the illustration here, I am choosing to save the best quality file, but it will be the largest. I could change my choice by moving the slider, entering a different number, or choosing a quality other than “maximum”. This illustration is from the Photoshop program. Different programs offer variations on this, but the result is always that you are making a choice between quality and size of file.

Jpeg quality versus file size

Note: merely viewing your jpegs (as opposed to editing and then saving them) will NOT degrade the image. And neither will time! Real, hard copy photographs do degenerate over time as chemical processes take their toll. Digital images on your computer will not suffer this fate.


Images as Email Attachments

If you are intending to send an image file as an attachment to an email then size matters. An image of acceptable quality saved as a jpeg could be 200kb or smaller, whereas the tif equivalent could be 20mb. The former would be perfectly acceptable as an email attachment, whereas the latter may not be delivered. As far as emailing jpegs is concerned, you can almost always save the jpeg at its highest quality and still have a file that will comfortably go through the email system. You can see in the first illustration that the file I am saving here would be 153.0k. This would be perfectly acceptable as an email attachment.

Quick reminder on file sizes: there are approx 1000kb in 1mb (one thousand kilobytes in a megabyte). An email attachment can be 5mb without causing problems and some email systems can handle attachments up to 20mb. Therefore, any file size that is expressed in kb (and is less than 5000kb) is less than 5mb. Therefore, any file size expressed in kb (provided that it is less than 5000kb) will be ok to send by email.

The Best of Both Worlds

If you only intend to edit a photograph once or twice then it’s probably OK (quality-wise) to save it each time as a jpeg. The quality will remain acceptable and it won’t cause problems by being too large. If, on the other hand, you are going to do a lot of editing, spread over several sessions, then it is worth getting to grips with how you can save an image in a “lossless” format such as tif or bmp, so that it doesn’t degrade each time you save it. When you have finished editing it you can save the final version as a jpeg so that you then get the benefit of compressing it without all the intervening stages of degradation. If you do this, by the way, you will finish by having a file in each of the jpeg format and the “lossless” format.

Whatever program you are using to edit your pictures, the way to save an image file in a different format is to find the command to “save as” (as opposed to the “save” command) and then look for an option to allow you to change the format. This illustration is from Photoshop:

Saving a file in a different format

In this instance, clicking on the triangle to the right of the “Format:” line offers many options for saving the file in a different format, including tif. When you have finished all the editing and want to create a final, smaller, jpeg file then just issue the “save as” command again and choose jpeg as the final format.

Zipping Image Files

Files can usually be compressed into smaller sizes by putting them into zip files (or other compressed formats such as rar). These can then be sent more easily through the email system. Zipping also has the advantage that only one file is sent, so it is easier to handle than trying to attach, say, 20 photograph files. The recipient then “unzips” the file back into its original components.

There is no reason why you cannot put jpeg files into zip files, but you won’t save much space. The jpeg has already been optimised, so the process of “zipping” it won’t squash it much more – if at all. Zipping “lossless” files (such as tif files) will reduce the overall size considerably and won’t compromise the quality of the image.

Having said all that, there are now many alternatives for showing other people your digital photographs that don’t involve trying to send them through the email system, so if you regularly send lots of images it’s worth considering them. These alternatives include posting images on your social media page (eg Facebook), storing them online on Microsoft’s Skydrive system or Kodak’s online photograph album system, or even creating your own photo website.

There are lots of other aspects of digital images that we could look at, so I think we will be returning to this subject before very long.

In the meantime, you can find more information on jpegs here.

If you have an older version of Microsoft Office (Office 2003, Office XP, Office 2000), or just an individual component of one of those packages (eg Word or Excel), then you may have difficulty reading documents created by newer versions (Office 2007 and Office 2010). To put the boot on the other foot, you may have emailed a document of the newer type as an attachment, only to have the recipient tell you that they can not read it.

That is because the structure of the documents changed with the 2007 version.

File Extensions

Depending on how your installation of Windows is set up, you may or may not see the “file extension” of each file when you view a list of files in Windows Explorer. The file extension is the part of the file name that comes after the full stop. The file extension tells Windows what type of file it is and Windows maintains a list of which program is used with each file type (in Windows jargon, each file type is “associated” with a specific program).

In Office 2003 and before, Word files had a file extension of .doc (eg “Letter to Father Christmas.doc”). Excel spreadsheets were .xls files (eg “Scalextric Costs.xls”) and PowerPoint files were .ppt files (eg “Pitch to Father Christmas For A Scalextric Set.ppt”).

From Office 2007, Word files have become .docx, Excel files are .xlsx, and PowerPoint files are .pptx. These file types are not compatible with earlier versions of the programs.


If you have one of the newer versions of Office then you have no problem in opening, viewing and editing files created in an earlier version. However, if you have an earlier version you can not open files created in a later version.


Save As

If you have a later version, and are preparing a document for opening on an earlier version, then the simplest solution is to create a version of the document that is in the format of the earlier version. To do this, open or create the document and then use the “save as” command instead of the normal “save” command.

Normally, the different ways of saving a file are as follows:

  • Use the shortcut key combination of Ctrl s (hitting the “s” key while simultaneously holding the Control key down).
  • Click on the little blue icon of the floppy disc that is probably visible on the top line of the screen.
  • Click on the “Office” button and then click on the “save” command.
Office Button

Office Button

Each of these methods will save the file in the newer format. What you need to do instead is to click on the “Office” button, then take the “save as” option, and then take the “..97-2003 document” sub-option (as illustrated). The recipient of your file will then be able to use it as if it had been created in the earlier version of the program.

file save-as dialogue box



I’m having to give up my previous practice of always quoting hyperlinks in full as some of them are just too long. If you are viewing this as a post on the blog then, depending on your internet browser, you can probably see the full version of the link if you hover your mouse over the link and then look towards the bottom of the browser window. If you are viewing the newsletter version, then hovering your mouse over the link should show you the full address of the link.

@ sign bouncing on a trampolineThis is a continuation (and conclusion) of last week’s post.

More clues to look for in the text of the (rather cryptic) bounce message

Unable to relay or relaying prohibited

There could be several reasons for this message:

  • Your email connection might require authentication by logging onto your incoming server before attempting to send anything out (a setting in the email configuration if you use an email program such as Windows Live Mail)
  • The smtp mail server (ie the outgoing or sending server) that you are trying to use will not allow you to use it as your IP address does not identify you as a legitimate user of that server (for instance, if you are using a laptop with a wifi connection other than your own router at home)
  • The return address of the email message is at a domain other than that of the smtp server


There are dozens of lists on the internet containing the names of servers that are known or suspected to send spam. Your own ISP’s email servers could have got onto one or more such lists. Although completely innocent, your email may be failing to reach its destination because the recipient’s email server found your ISP’s email server on a blacklist they check against.

If this happens to you, you need to contact your ISP, explain that you think they’re on one or more blacklists and ask them to act to get themselves removed. A client of mine fell foul of this problem a few months ago. The reaction of the ISP was somewhat underwhelming in that they said they had tried to get removed but it was outside their control. Not very useful. In the end, we took advantage of a facility provided by Google whereby you can retain your own email address but have your messages routed through Google’s servers. Free of charge and it’s been working ever since (but a bit messy to set up).


This is not as serious as blacklisting. What it means is that the recipient’s email system will only receive email from specific (ie “whitelisted”) email addresses. You would need to contact the recipient by a means other than email in order to get your email address added to their whitelist.

Spam Filters

Look in the bounce message for words such as “blocked” or “suspected spam”

Your email may have been rejected by the recipient’s server as it looked like spam. There are certain things you must avoid when composing emails – eg don’t write in capital letters, don’t use multiple exclamation marks. I was just about to give specific examples of what not to do but then realised that the newsletter version of this blog post would probably get caught up in everyone’s spam filters. The reality, though, is that you are unlikely to know that your message has been rejcted for being suspected as spam. Spam messages aren’t normally bounced – just discarded or held in quarantine.

Non-Delivery Without Bounces

There are times when the recipient claims not to have received your email but you did not receive any bounce message. There are several possible causes of this:

  • Spam Filters – If your email has been blocked by a spam filter then you may not be informed by a bounce message. Your message will seem to have simply disappeared into the ether.
  • Junk Folder – The recipient’s email software (as opposed to the recipient’s email server) may have intercepted your message as spam and moved it directly to the recipient’s Junk folder. So if someone says they haven’t received your email the first thing to do is ask them to check their Junk folder.
  • Email Rules – The recipient may have set up their own rules in their email software to semi-automate the handling of incoming mail. One of these rules may have caught your message and dealt with it in an unexpected way. If you have reason to suspect this, you might ask the recipient to to perform a Windows search on some specific text in your email. If the message is in their system but has been moved somewhere unknown by a rule or filter then this may explain what’s happened.
  • Message or attachment too big – If you suspect this is the problem, try sending a short email with no attachment. If it gets through then it may have been that the incoming server rejected your message because either the message or an attachment was too big. Some email servers won’t accept attachments bigger than 5mb, others 10mb. If I’m sending someone a large attachment I always ask them to confirm receipt.

Conclusion: although bounces are a nuisance, the bounce messages often contain useful information – you just need to glean the information and ignore the machine-speak.

@ sign on a trampoline - bouncing email…..and what you can do about it

What is a Bounce?

If an email message can not be delivered to the inbox of its intended recipient then it is said to “bounce” – ie the sender receives a message advising that delivery failed.

Bounces that aren’t

The first thing to do when you receive a bounce message is to identify the message that wasn’t delivered. There will be a reference to it in the bounce message. If there is no reference to any message originated by you then be careful as this may be spam or a virus and not a bounce at all. In particular, don’t open any attachment if you’re not sure that this message is actually a bounce relating to a message you sent.

Another possibility of a bounce message that did not originate with a message sent by you is known as “backscatter“. Spammers are able to make their messages look as if they came from completely innocent and legitimate email addresses (eg yours). If the spam they send out is bounced back then you will receive that bounce even though you had nothing to do with the original message. It’s an unsettling experience, but all you can do is delete the bounce message.

Real Bounces

A real bounce will refer to a message you sent. If it is a “hard bounce” (the message was rejected by the email server to which it was sent) then you will probably receive the bounce within a minute or so of sending the doomed message. If it is a “soft bounce” (accepted by the email server but ultimately undeliverable to the recipient) then it may be days before you receive the bounce as the server may have made several attempts to deliver it.

To determine what you can do about a bounced message, you need to look for intelligible phrases in the bounce message:

Some common phrases to look for amongst the gobbledegook are:

user not found
not our customer
mailbox not found

All of the above – and others like them – are suggesting that the recipient’s server accepted the message but then couldn’t deliver it to the user because there is no valid user with that username. The username (more properly known as the “local mailbox part”) is the part of the email address before the “@”, so in “” the user (local mailbox part) is “fredsmith”. The cause of this error is very likely to be just a spelling mistake or typo (wrong key hit) on your part. Alternatively, the email account may have been closed so that email address won’t accept any more messages.

The pedant in me insists that I point out that, in theory, the local mailbox part is case sensitive. In other words “FredSmith” is not the same as “fredsmith”. In practice, I have never come across an email failing to get through for this reason. Bizarrely, the “domain name” part of the address (the part after the “@”) is not case sensitive, so “” is the same as “”.

If the bounce message includes a phrase such as

quota exceeded or
mailbox full

then the user has filled up the disc space that they are allowed to use for email and must move or delete some of it before they can accept more email. If you need to get your email through then it’s often quickest to phone the recipient so that they can do something about it. This is an example of a soft bounce. The server may attempt to deliver the message for two or three days before telling you that it failed.

Another common explanation for a bounce is given as

Host unknown

This either means that the domain name (the part of the address after the @) is incorrect or the server of that name is unavailable. For example, the “” part of the email address “” may be incorrect. Check that you’ve got the email address correct and try again. It could just be that the email server is temporarily busy or unavailable. In that case, sending the message again may result in a normal delivery. If I’ve been having a problem like this, but then the message doesn’t bounce on a re-try, I will sometimes send another message asking the recipient to confirm delivery of the first one. If, however, your second attempt results in a second bounce and you are sure that the address is correct then try a bit later (say, an hour or so). If you haven’t managed to get it delivered in a day then it’s probably best to contact the recipient.

There are other reasons for bounces and sometimes a message doesn’t seem to reach the recipient even though you don’t receive a bounce. I’ll be returning to this topic next week.

Have you ever had trouble sending a large email attachment? If you try to send an attachment that is too big then you may find that it bounces back to you (ie you receive a message saying that the message could not be delivered). The limiting factor may be in the recipient’s email system or in a system that the email (with attachment) has passed through on the way to the recipient.

You are not likely to encounter this problem if you are just sending average-sized spreadsheets, word processing documents or pdf files, but “media files” such as video clips, sound files, and many high-resolution picture files can very easily be far too big to send as attachments.

Large AttachmentsHow do I know the size of an attachment? This depends on the email system you are using. In Hotmail, for example, after you have added the attachment to the email you can hover your mouse over the attachment and a small box will pop up that includes the file size (eg 273kb). With most other systems the size of the attachment is shown in brackets after the name of the attachment.

What is the maximum size of an attachment? Hotmail is supposed to be able to receive 10mb attachments, Yahoo and Gmail have a limit of 25mb. These are all webmail systems. If you are using POP-based email (eg you check your email using Outlook or Windows Live Mail) then there is probably a limit set by the email servers you are using. If you have your own domain name then you are probably using your domain host’s email servers. Otherwise, you will be using your ISP’s servers. The limit they impose can be as low as 5mb. Also, the theoretical limit of a Gmail attachment is 25mb but the actual file sent through cyberspace is larger than your original file by up to about 20% so Gmail’s actual maximum is probably nearer to 20mb. Anyway, even if you know the limits of your own system, that doesn’t help in telling you what your correspondent can receive as that depends on their system rather than yours. Personally, I would not assume that an attachment of over 5mb is going to go through without trouble. I always check with the recipient that they have received anything I have sent bigger than 5mb. Note: there are 1024kb in 1mb, so if your attachment size is expressed in kb rather than mb then anything less than about 5000kb is less than 5mb and will probably be delivered without problem.

What can I do if my attachment is too big? There are several options:

  • split the file up into smaller pieces. There is software available for splitting and rejoining files. I don’t recommend this method.
  • compress the file into a (smaller) zip file. This can work very well for some file types (eg tif files) but not have very much effect on others (eg jpg picture files, that are already optimised for the trade-off between size and quality). Zip files are a good idea, by the way, if you are sending many attachments as they can all be sent in one zip file for unpacking at the recipient’s end.
  • use an online service such as

Using GoAruna, you don’t even have to register if you just wish to send a single file. All you need to do is enter your own and the recipient’s email addresses and upload the file you wish to attach. The recipient is then sent an email with a link so that they can download the file. Although there is a time limit (seven days) on the availability of the download, this method does have the advantage that the download is under the control of the recipient. This can be better than having their email system tied up while a large attachment download takes place (although this is becoming less important as internet connections become faster). A single file sent this way by GoAruna can be up to 100mb. By registering with Aruna, you can also have 2gb of online storage. This can be used for backups and/or making files available to other people that may otherwise have needed to be sent as email attachments. Note: just as there are 1024kb in 1mb, there are 1024mb in 1gb.

There are other services similar to GoAruna. You may like to look at these:

The normal place to enter the email address of the recipient of your emails is the “To:” field (a “field” in computer terms is an area in which data is stored). You can send the same message to several people by entering all their email addresses here (separated by commas or semi-colons). Every person receives the message and every person sees the email address of all the other recipients.

Email address fields

So what is the CC field?

This stands for “carbon copy” and goes back to the days of typewriters and carbon paper. Someone who is “cc’d in” receives a copy for their information. All addresses entered in the CC field are also visible to all recipients of the email.

And what is the BCC field?

This stands for “blind carbon copy”. Other recipients are not aware that someone else has received a “blind copy”.

But I can’t see a BCC field!

Different email programs are set up differently and a lot of them do not display the “BCC” field by default. If you can’t find how to display it in your own email program tell me what email program you are using and I will see if I can help.

But why use the CC and BCC fields?

Well, the difference between the “To” and “CC” fields is that the “CC” recipient is just being informed (or, as they say tirelessly these days, “kept in the loop”). They are not expected to respond in the same way as the main recipient. This is actually causing big problems in a lot of organisations where people send “CC’s” to all and sundry so that they can say they kept the other person informed. Consequently, people are being bombarded with emails that they have to read in case there’s anything they actually need to know.

The first use of the BCC field is fairly obvious – you can send someone a copy without anyone else knowing.

However, there is a much more important use for the BCC field. Suppose you want to send the same email to, say, 30 people who do not know each other. If you put all their email addresses in the “To” field or the “CC” field then they will all see each others’ email addresses. This is fine if everyone on the list already knows everyone else, but it’s a very bad idea otherwise. To begin with, it’s bad “netiquette”. By displaying someone’s email address to other people you are opening up the possibility of that email address being abused (by spammers, for example). Would you give out someone’s phone number to other people without permission to do so? I have also heard that it is possibly a contravention of data protection legislation to be cavalier with email addresses in this way. I’ve no idea whether that’s true or just an urban myth, but I’m sure you get the point.

So, if you wish to send an email to lots of people without revealing their addresses to each other you put them into the BCC field. If you do this you must still put an address in the “To” field and the easiest thing to do is to put your own address here. You could also create a contact in your email contacts/address book that consists of your own email address with the “display as” information set to “undisclosed recipients”. You then use this as the recipient in the “To” field.

While we’re on the subject of netiquette, there are a couple of options in most email programs that are useful if used sparingly, but which drive me (and others) nuts when overused:

  • prioritising emails – by all means put a “high priority” tag on emails that require a high priority response, but don’t put one on every email. I’m sure I’m not the only person childish enough to treat these “me, me, me” emails with a slower than average response.
  • requesting a “read receipt” for every email. As a matter of bloody-minded principle, I refuse to send “read receipts” to people who request them on every email they send me. Anyway, I think I’m intelligent and mature enough to be able to work out for myself when it is appropriate to acknowledge receipt of an email.

Grumpy? Moi?

Ok, I don’t deny that I can be a bit pedantic at times (the rogue apostrophe, for example), but shouty emails irritate lots of other people as well as me, and even seem to have got at least one person the sack – see this item in The Telegraph, for instance.

What’s a shouty Email?



Email is much less formal than, for instance, writing letters. Nevertheless, you don’t have to be as pedantic as me to be put off by emails that irritate, confuse or upset the recipient by the way in which they are written. There are some “rules” (or, shall we say, “guidelines”) that have grown up around this subject and they go under the name of “netiquette”.

And it’s not just a case of violating netiquette. Spam filters treat manic capitalisation and punctuation as indicators of spam so, ironically, your efforts to really get your point across by SHOUTING could undermine the chances of the message even being delivered.

© 2011-2019 David Leonard
Computer Support in London
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