Max line length in mail

Question

Why is the php documentation of mail() saying

Lines should not be larger than 70 characters.

(under the part: parameter message

Answer 1

The Internet Message Format RFC the latest of which is 5322

2.1.1. Line Length Limits

There are two limits that this standard places on the number of characters in a line. Each line of characters MUST be no more than 998 characters, and SHOULD be no more than 78 characters, excluding the CRLF.

...

The more conservative 78 character recommendation is to accommodate the many implementations of user interfaces that display these messages which may truncate, or disastrously wrap, the display of more than 78 characters per line, in spite of the fact that such implementations are non-conformant to the intent of this specification (and that of [RFC2821] if they actually cause information to be lost). Again, even though this limitation is put on messages, it is encumbant upon implementations which display messages

(The MIME RFC also specifies a max of 76 characters)