feat: Add date to email headers in Send function

[blib]

Implement 'Date' header to comply with email RFC standards and enhance deliverability by satisfying spam filters.

[dbarrosop]

Thanks for the PR. Which RFC are you referring to? And how does this improve deliverability? Any sources you can link to?

[blib]

The RFC 5322 states in section 3.6.:

The only required header fields are the origination date field and
the originator address field(s). All other header fields are
syntactically optional.

Many spam filters, like SpamAssassin and Amavis, have rules that flag emails missing the required "Date" header as potential spam. I've noticed instances where emails ended up in spam folders with the header X-Amavis-Alert: BAD HEADER SECTION, Missing required header field: "Date" due to this issue.

[dbarrosop]

Perfect, thanks for the added info.