Parse an SMTP (RFC-5321) address.
** Changes in version 1.1.0: **
** Domains are now checked beyond RFC-5321 syntax only **
Domain names must be fully qualified; that is with at least two labels. The top-level domain must have at least two octets.
** Length limitations are now checked **
Total length limit of an address is 986 octets; based on a 1,000 octet SMTP line length.
See https://tools.ietf.org/html/rfc1035 section 2.3.4. Size limits:
Domain names are limited to 255 octets, when encoded with a length byte before each label, and including the top-level zero length label. So, the effctive limit with interstitial dots is 253 octets.
Labels within a domain name are limited to 63 octets.
The above are limits of the DNS protocol, not any particular implementation.
RFC-5321 section 4.5.3.1. “Size Limits and Minimums” still says:
“To the maximum extent possible, implementation techniques that impose no limits on the length of these objects should be used.”