Allow formatting of BCC addresses

[LhKipp]

Hi karastojko,

thanks for the library. I've seen commit 1124e1e removes formatting of the bcc addresses.

I believe the commit has been added, because when one email-server sends the email to another, the bcc address should be excluded.

However we at PPRO are sending the email - formatted as a mime message - from our application to AWS-SES. AWS-SES will parse the mime message and retrieve the destinations from the to,cc,bcc headers. AWS SES will omit the bcc addresses on sending them to the destination mail servers.

For our use case it would be beneficial to format the bcc address. Would you be okay, with me opening a PR to make adding the BCC address to the formatted message configurable? E.G.:

msg.format(buffer, true /*dot_escape*/, true /*add_bcc_header*/)

or

mailio::message::format_options opts {.dot_escape = true /*default false*/, .add_bcc_header = true /*default false*/};
msg.format(buffer, opts);

Thanks for your time and effort 👍🏻

[karastojko]

Hi Leonhard, Thanks for the explanation. Sure, let's make a PR and discuss it. I was also looking into the SMTP specification for these headers. The bug looked to me critical, so this was the fastest fix. Probably it could be improved.

Thanks

[karastojko]

PR merged. Thanks a lot!