>Anyone would know the regulation for the maximum length of a subject in an email? Is it something general or specific to the mailer/servers? I have an email which I need to include specific IDs in the subject and this one is quite long. I am have 134 character so far and this is accepted. However, do I have a guarantee that this will make it to the destinator?

Found a relevant discussion
http://stackoverflow.com/questions/1592291/what-is-the-email-subject-length-limit

and also

http://www.networkworld.com/newsletters/2010/060710web1.html

A subtle but crucial issue in the use of email and one that marketers often neglect is how long a subject line can and should be. The answer to "can be" is defined in RFC 2822 which states that "There are two limits that this standard places on the number of characters in a [email message] line. Each line of characters MUST be no more than 998 characters, and SHOULD be no more than 78 characters, excluding the CRLF."


Now the "should be" part: The 78 character limitation has been ignored by many online services who only allow much shorter subject lines. The result of this is that subject text will be truncated to whatever arbitrary maximum length they permit.