Google Groups Invites not being received

At work we've been getting a lot of people reporting that they've been invited to a private google group but haven't received the invite. The Group moderator says they sent the invite but the recipient never received it.

It took a while but I think I have an answer. At least, I have a fix if you are using Trend Micro IMSS to check your mail before it is delivered to your internal mail servers.

It might be to do with the length of the email address that google's server uses to send the invite.
As soon as IMSS started to receive the invite email, it would drop it as invalid.

The invite email header's MAIL-FROM address was: "grbounce-v69lOAUEAEBnNWTkA5m_texcgVeUF-2Q=xxxxxxx=xxxxxxxxx.org.uk@googlegroups.com"
(I've replaced my details with x's above)

According to the official RFC (#3696) the part of the address before the @ sign must be no longer than 64 characters long.
The Google Groups invite email was 66 characters long, so our mail server was rejecting them as invalid.

“In addition to restrictions on syntax, there is a length limit on
email addresses. That limit is a maximum of 64 characters (octets)
in the "local part" (before the "@") and a maximum of 255 characters
(octets) in the domain part (after the "@") for a total length of 320
characters. Systems that handle email should be prepared to process
addresses which are that long, even though they are rarely
encountered.”

Extract from page 6 of RFC3696: http://tools.ietf.org/html/rfc3696


To stop IMSS checking the length of the MAIL-FROM address we added the following line in tsmtpd.ini in the [SmtpServer] section:

CheckSenderLength=0

Hope this helps someone!