Encode period at start of line

[chuckwagoncomputing]

For some reason I don't quite understand, a period at the beginning of a line is special.
Other email clients don't encode periods unless they are at the start of a line, so that's the example I followed here.

I'm not sure if it's possible for a period to be at the beginning of a line without being wrapped there, but I checked for that just in case.

I found this bug because it was deleting a period from a URL, breaking a link.

P.S. I'm new to Elixir so I welcome your correction

[andrewtimberlake]

A period at the beginning of a line is valid in an email body.
If a period exists on its own in a line, then the period will be doubled during an SMTP transmission (because a sing period followed by \r\n indicates the end of the transmission)

[chuckwagoncomputing]

Then in your opinion the bug is in the SMTP client (swoosh mua adapter in my case)?

[andrewtimberlake]

When transmitting over SMTP, a line starting with a period should have a period added to the beginning.
When receiving over SMTP, a line received with a period at the beginning, not immediately followed by \r\n, should have the leading period removed.
See https://www.rfc-editor.org/rfc/rfc5321#section-4.5.2
It may be that the mua adapter is not adding the period during transmission. It depends on where in the process you’re picking up the problem.