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Is there an upper limit on the number of attachments one can send in a single e-mail message? I am coding an application to act as an e-mail forwarding service which receives delivery requests and stores them in a database for later dispatching, and it would come in very handy if I knew beforehand that sending more than, say, 32 attachments is not supported by the e-mail protocols. Is there any such limit?

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What client are you useing to send emails? – ben950 Nov 10 '11 at 11:00
It will be a given SMTP server about which I know nothing at this point. – DotNetStudent Nov 10 '11 at 11:03
I know that there is a list of RFCs which talk about things such as maximum length of e-mail addresses and so on, but I can't remember the number right now. I'm sure that they would be the correct place to look for canonical answer. – AndrejaKo Nov 10 '11 at 11:07
If I'm reading the FRC 5321 correctly (section seems relevant), then there should be no limit to number of attachments in an e-mail. Any limit should be only imposed by implementation. – AndrejaKo Nov 10 '11 at 11:20
True, but the majority of ISP's have their own interpretation of this as they each have their own spam servers... I'm suffering from one at the moment who has set a (low) limit to the number of emails you can receive in an hour... ARGH! – HaydnWVN Nov 10 '11 at 12:08

As @AndrejaKo identifies rfc5321 states there should be no limit to the number of attachments in theory but implementations may vary as @HaydnWVN points out. More likely to hit the limit for the email size (e.g. Virgin Media will return emails larger than 20MB and GMail limit is 25MB)

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