client: add new functions to specify options

[rjarry]

Expose a new set of functions to create a client with custom options.

[rjarry]

Hi @emersion, do you have any remarks?

Since the 0.21 release, it is not possible to connect with STARTTLS and a custom local name other than localhost. Some MTAs enforce clients to expose their real hostname and reject email when the HELO contains a non FQDN.

send:: conn.Rcpt: SMTP error 504: <localhost>: Helo command rejected: need fully qualified hostname

If this PR could be applied and included in a tagged release it would be awesome :)

Thanks!

[emersion]

This commit should already fix your issue: 75e52af

This PR adds a more convenient way to set client options but doesn't add any new functionality - I'm not 100% sure it's a good idea to have 2 ways of doing the same thing...

[rjarry]

Ok, this should do fine. However 75e52af it is still on master, not included in any tag yet. Could you cut a 0.21.3 version including this?

Thanks!

[emersion]

This was more tricky than just releasing a new bugfix release, because master also has another commit with breaking changes. I've established a branch for v0.21.x and released 0.21.3.

[rjarry]

Thanks!

Should I close this PR or are you considering taking it in?

[emersion]

Yeah, please keep it open.

If I had to design an API from scratch, I'd probably only expose options and not expose public fields in Client.

[JokerCatz]

the default timeout toooooo long, we need this PR or something like this