RFC 3696, "Application Techniques for Checking and Transformation of Names", February 2004

Errata ID: 1003
Status: Verified
Type: Technical
Publication Format(s) : TEXT
Reported By: John C. Klensin
Date Reported: 2005-07-09

Section 3 says:

   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.

It should say:

   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. However, there is a restriction in RFC 2821 on the length of an
   address in MAIL and RCPT commands of 256 characters.  Since addresses
   that do not fit in those fields are not normally useful, the upper
   limit on address lengths should normally be considered to be 256.

   

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