Email Size Limits

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How big an email is too big and what do those bounce messages mean?

Most email messages are small, at least when there’s just text.  Even a long HTML formatted message with no images or attachments is rarely more than 200kb – which is tiny by today’s standards.

Add an image or other file and that can grow to 1,000 or 2,000kb very quickly (roughly 1MB or 2MB).  Even that should not be a problem these days.

However if you include several files then the email size can grow to a size that becomes a problem for the receiver’s system.  Some files from a digital camera can be 4MB or more and that starts heading into the danger zone.

The size of the message includes the text and the message header, not just the attachments.  Usually the text and header are quite small but it’s worth keeping in mind.  An email attachment near a size limit can be taken ‘over the top’ by the other text in the email.

Generally speaking the file attachment size will match the email attachment size, but this wasn’t always the case.  In the early days of email, attachments used a UUencode system to send attachments with effectively doubled the file size in order to send it. 

These days more efficient encoding systems are used and most people don’t worry about it; and they use the default settings.  For example, Outlook has an option to use UUencode for plain text messages with attachments but the default setting is off and it’s best to leave it that way unless you really need to change it.

Maximum Message Size

There is no hard rule for the maximum size of a message that can be accepted by a mail service.  It very much depends on the receiver’s email service – it has nothing to do with the email program settings of either the sender or receiver.  Some ISPs make their limits clearly known (like 10MB for Gmail) while other ISP’s seem to treat this information like a corporate secret.

Usually the size limit applies to both incoming and outgoing messages, though they can vary.  It’s possible that outgoing messages have no limit but incoming messages do.

Rarely an Internet provider sets a limit for the accumulated size of incoming messages over a day, week or month – happily this is a rarity though in one case we have to email attachments just after midnight (their time) in order to make use of a new day’s email limit.   If your email service does this, it’s time to send a complaint letter or switch to another company.

Size of mailbox

Another related possibility is that your large email takes the receiver’s emails above their total mailbox size limit.  For example you send a 7MB email to a mailbox that has only 5MB of free space available – your message will be refused because it can’t fit in the receiver’s available space.

This can happen for people with small mailboxes (common with some of the older free webmail services) who also don’t check their email very often.  People in this situation might consider switching to a more generous service like Google’s Gmail with 2GB plus of email storage.

Generally the receiver gets no warning that an incoming message was refused so you have to send a short email, contact them some other way or wait until the mailbox clears.

‘Bounce’ message

An email from the mail service saying that your email was refused is commonly called a ‘bounce’ message (because your message is being bounced back).  Sadly there’s no common format to these messages and they don’t make a lot of sense to most carbon based life forms.

Here’s an example of one we received last week (with names and domains changed) – we’ve highlighted the parts that are important.

From:  System Administrator

Subject: Undeliverable: Emailing: Orange netting.JPG

Your message did not reach some or all of the intended recipients.

      Subject:       Emailing: Orange netting.JPG,
Sent:   19-Jun-2006 11:33 AM

The following recipient(s) could not be reached:

      [email protected] on 19-Jun-2006 11:34 AM

            This message is larger than the current system limit or the recipient’s mailbox is full.  Create a shorter message body or remove attachments and try sending it again.

            Msg Size greater than allowed by Remote Host>

The bounce message isn’t precise about the problem, though we know its something to do with the size of the message.  The second part (after the SMTP error code) says that the message size is too big but the earlier sentence suggests it could be either the message size or the mailbox is full. 

Typically the bounce message isn’t too helpful, it would be nice if the email stated the size limit for incoming messages (that would be a courtesy for both senders and receivers) but it rarely happens.

Again, this is the message sent back to the sender.  The receiver (ie owner of the mailbox) doesn’t know that a message was refused delivery to his/her mailbox.

(In this case we called the receiver, who confirmed that his mailbox was clear so we resent the message with a smaller attachment).

Rule of Thumb

As a rule of thumb, any message less than 10MB should be OK to send.  That’s the limit for Gmail and, as a result, it is becoming widely accepted by other email services.

But 10MB can be too large for some receiver’s email services.  In the example above we still don’t know the limit but it seems to be around 6-7MB.

What is the limit?

The obvious thing to do is ask the receiver what the limit is for incoming messages on their mail account.  Sadly most people don’t know and find it hard to get an answer from their email service, or perhaps they could not be bothered to find out.

Even worse you’ll get a nonsensical answer.  We’ve been told ‘the limit is 1GB’ which is really the total mailbox size not the individual incoming message limit.

You can try to investigate for yourself if the email address is a common domain – for example if the receiver’s address is you can go to that web site and surf around.  (the answer is 5MB with a 125MB total mailbox size depending on the type of account, and there’s no way to tell that from the email address alone.  Outgoing emails seem limited to 5MB, no mention of an incoming size limit)

Know thy message limit

There’s nothing much that you can do about other people’s ignorance but you can find out the answer for your correspondents.

Go to the support site for your email service (or ISP if they supply your mailbox as well) and find out the limits:

  • on your mailbox (ie maximum mailbox size)

  • size limit for incoming email messages

  • size limit for outgoing email messages

  • any other limits 

If those limits aren’t published then contact the service and ask for clarification.  Ideally get it in writing/email because often the phone support people don’t know and will blow you off with the wrong answer or just a guess.

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