550 Nul message

[WhippingBoy]

I have a customer that gets returned mail when sending to only a couple of addresses. When she sends an email it is returned with the following error:

Reporting-MTA: dns; mailin02.something.com

Final-Recipient: rfc822;something@something.com
Diagnostic-Code: smtp; 550 Requested action not taken: NUL characters are not allowed.
Remote-MTA: dns; x.x.x.x
Action: failed
Status: 5.0.0

This does not happen with every email only certain ones. And has only started happening in the last week.

TIA
Rich

 

[kalmanTRF]

Came across your post in my own search for a solution to this problem. This is what I have surmised as of now.

It's a feature of Outlook (or Microsoft or MAPI). There are two standards involved here, the SMTP standard used for sending email and the IMAP4 standard for receiving mail. The SMTP standard says you can send any ASCII character in a mail message (that's character codes 0-127). The IMAP standard says it will accept any character code between 1 and 255.

For some reason, Microsoft inserts a NUL character between attachments, why I am not sure. However, it is a legal thing to do as SMTP allows an ASCII 0 character (NUL). With that being said, their system should accept it. If they are using IMAP to read their emails they will, however, not be able to read it. Thus the reason they probably reject it in the first place. The conundrum is that both parties are doing things that are correct, it is just that there is a different correctness between IMAP and SMTP.

With that being said, anyone know if there is a way to stop Outlook (or watever is doing it) from inserting a 0 in the emails?

Thanks,

Ken