Mail error 550 Maximum line length exceeded (RFC 5322 2.1.1)

Dennis asked:

I have a reseller hosting account containing a couple of domains. One of our clients has recently been complaining about emails not being sent. They are receiving the error "550 Maximum line length excxeeded (RFC 5322 2.1.1)".

After some Googling it appears that the maximum length can only contain 998 characters (+ line breaks). And upon inspection of the .eml file of the email, i can find two lines each containing over 1000 characters. So indeed, this is where the problem resides.

However, i’ve tried contacting my hosting provider and try to determine where the problem is exactly located on an architectural level and how it can be prevented. But it seems they’re completely clueless themselves (or don’t want to admit it).

Our client having the issues, uses a very specific software (Bouwsoft) where they manage their emails and sent their emails from. Bouwsoft uses the IMAP settings of our reseller hosting email server in order to pull the mails and sent the emails. So everything goes via the reseller mail server.

So the main question boils down to: is it the responsability of the mail server of our hosting provider to split the long lines in the email to not contain more than 1000 characters, or is this the responsability of the software which sends the emails (Bouwsoft in this example) ?

Thanks in advance!

My answer:

The software which creates the email and submits it is responsible for ensuring that it complies with all relevant standards, such as not having excessively long lines. The mail server is rightly complaining because the software did not do so.

There is nothing that the mail server can (or should) do about this. This is the responsibility of the software which created the message to fix.

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