Most developers of early mainframes and minicomputers developed similar, but generally incompatible, mail applications.
Over time, a complex web of gateways and routing systems linked many of them.
RFC 5322 replaced the earlier RFC 2822 in 2008, and in turn RFC 2822 in 2001 replaced RFC 822 – which had been the standard for Internet email for nearly 20 years.
Some non-ASCII values may be represented using MIME encoded words.
Email header fields can be multi-line, and each line should be at most 78 characters long and in no event more than 998 characters long.
Each message has exactly one header, which is structured into fields. The field name starts in the first character of the line and ends before the separator character ":".
The separator is then followed by the field value (the "body" of the field).
Selector .selector_input_interaction .selector_input. Selector .selector_input_interaction .selector_spinner.