I'm using Zend_Mail to send emails. Few articles (like first example on this page) have suggested to wrap long lines in message body.
Questions:
Is it necessary to use wordwrap(), in case any of line is larger than 70 characters?
Where does this '70' figure come from?
RFC 2822 and 5322 have a sections called Line Length Limits (2.1.1):
Sounds to me like the real limit is 998 characters and 78 is something that you don't really need to bother with.
AFAIR, the 70 ~ 78, more likely a "save" version of 80, comes from good old terminals, which displayed 80 characters per row. In the very early days these terminals were just dumb printers that needed their output prepared on the server. This 80 in turn comes from good old punchcards. The punchcard's physical size (and therefore somewhat closely related the 80 limit) comes from money trays, which were often used to store punchcards.
Humans and technology have a hard time getting rid of old habits. I recommend the first Crockford on Javascript talk for more history: http://yuiblog.com/crockford