Email message size limits


Prompted by a request from staff at a client’s head office, a couple of days ago i posed this question to a couple of the mailing lists i’m on: what is your size limit on individual email messages?

I was blown away by the speed, quantity, and quality of the responses i received from the AusNOG and SAGE-AU communities.  Within an hour i had some hard data and a useful recommendation to take to my client.


I’ve published the statistics and the raw figures to separate sheetes in the same Google Docs workbook; a few explanatory comments about the results are necessary:

  • A number of responses indicated two values, often broken down by receive/send or internal/external criteria (with the latter being the smaller).  This is indicated as “Tier 1” vs. “Tier 2” in the raw results.  I’ve used the “Tier 1” figure to calculate the results.
  • Answers which were ambiguous or indicated no limit were not included in the calculations, nor was one answer of 5 GB, since it skewed the results unrealistically.


  • Number of responses: 64
  • Number of numerically quantifiable responses: 57
  • Mean: 30.105 MB
  • Median: 25 MB
  • Mode: 20 MB
  • Standard Deviation: 20.929 MB

Bottom line

I’d say that anyone using something in the range of 10 – 50 MB could consider themselves reasonably “normal”; both those figures are within one standard deviation of the mean.


Here are some of the more interesting comments i received, along with the size they indicated.  In most cases, these are direct quotes, but i’ve edited them for spelling, clarity, and punctuation where necessary.  I’ve highlighted two responses that i found striking, given their closeness to the actual results.  (I also suggest reading the AusNOG discussion – both threads – some excellent points were made.)

Size(s) Comments
8 If people need to send more than that, email is the wrong answer.
15 We’ve found in the past increasing above 15 MB resulted in a large number of bounce backs for organizations rejecting messages that were too large being sent to them. The biggest issue we have is explaining this to our customers and them believing it. Mainly because they don’t understand that a simple 8 MB JPEG can blow out to 20-25 MB because of mime encoding etc. We try our best to advise them of this, we do get quite a lot of arguing and feedback requesting we increase it anyway. However, slowly they’re realizing: when their large messages start bouncing back they ask us to set the limit back to what it was before.
25 I imagine a general consensus will be 25 MB upper limit due to Google Apps.
25 Most of my clients have gone Google Apps.
30 Our general view is that if a limitation is lower than what a customer gets on gmail (which is currently 25 MB) and related free services, then you will need to support at least that limit. A limit of 30 MB doesn’t have to be in place long before user actively notice that the limits are typically elsewhere, and start talking about how good their system is. Non-technical high-ups will struggle with paying for a business service that offers less than their personal accounts.
30 Microsoft did a risk assessment for us and noted that having large message sizes and large mailbox sizes (10G to 60G) is a high risk.
40 … and we still get complaints.
50 People still run into [our limit.  We] had ‘someone’s IT guy’ tell us the ‘industry standard’ was 10 MB. I expect you’re getting a wide range of answers, and that there really isn’t an ‘industry standard’.
50 Unfortunately, I still get called every time an email bounces due to remote size limits.
100 We didn’t see any notable impact because of this change [to 100 MB], no delays, additional load or problems caused by the larger emails. Note: These clients had 20, 50, 100meg or faster Internet pipes.
5? I’m actually looking at reducing email size limits to force users into using technologies designed for file sharing and governance – Sharepoint, Skydrive Pro, etc. Reducing limits to 5 MB has all sorts of flow on effects: not even talking about freeing up link bandwidth, Exchange store sizes, etc. I’ve found that email enables poor habits. Emailing a 10 MB doc to the user 2 rooms down via a hosted exchange? Floods the link twice, plus stores the attachment in your local OST, the recipients local OST, and two copies in the exchange store. Now, modify it, and send it back. Ouch.
20? If I had to pick a single size that’s used, it would probably be 20 MB – but there’s no end of variation. 10 MB is common, although mainly for historic reasons, and the number of people with such a low limit is dropping. 25 MB and even 50 MB aren’t uncommon. 100 MB is rare, but out there – mainly in situations where mail is being sent to a specific recipient and they have also upped their [overall] limit. I’ve even seen one company who wanted their limit set to 1 GB…
unlimited/10 I can not express enough the frustration in a customer saying they want to send a bigger email and wanting us to up our limit, explaining the internet is just too hard a task sometimes. In one specific case it was an 11 MB email, the customer response was “It’s only an extra 1 MB can you just let it through this once”, so I pointed him to an SMTP with no limit on it; next day he is forwarding a bounce back from the receiving end who blocked him based on size.


For those who are interested in the decision: my client and myself were both previously part of the “10 MB is the industry standard” camp, but found the argument about gmail compatibility compelling, and have decided to increase to 25 MB, much to the delight of the staff member pushing for the change.


  1. Disclaimer: I am not a statistician; this is not a scientifically- or statistically-valid survey; all online polls are inherently bogus due to the respondents self-selecting; i have no idea whether this sample is statistically significant or valid; i did not attempt to authenticate or validate the responses in any way; YMMV; no warranties expressed or implied, etc.


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