Change smtp.MailOptions to a pointer

[kayrus]

Pass a pointer instead of the struct copy.
Will require a corresponding change in https://github.com/emersion/go-smtp-proxy

[kayrus]

I'm also thinking of parsing the from and rcpt emails via https://pkg.go.dev/net/mail#ParseAddress and return an error, if parsing is failed. Therefore we can pass a *mail.Address pointer to Mail and Rcpt methods instead of the strings.

[foxcpp]

I'm also thinking of parsing the from and rcpt emails via https://pkg.go.dev/net/mail#ParseAddress and return an error, if parsing is failed. Therefore we can pass a *mail.Address pointer to Mail and Rcpt methods instead of the strings.

NACK, mail.Address is for RFC 5322 header values, not SMTP envelope. What mail.Address represents and what mail.ParseAddress would accept is invalid for SMTP.

[foxcpp]

Wondering why this is not merged yet. Since we are breaking stuff all around we can probably merge this too.
@kayrus, can you rebase your PR on master?

[emersion]

Acked-by me

[kayrus]

rebased

[foxcpp]

LGTM (server example in README needs an update too but I will take care of it)