Notification mails do not have the required DATE header

[corneliusludmann]

My mail server (more precisely my amavis) does not accept the notification mails sent by keel because the required DATE header is missing (see RFC 822). I was able to work around this by setting the option always_add_missing_headers = yes in my postfix config so that postfix adds the missing DATE header. However, it would make sense that keel sets this header to be RFC 822 compliant, IMHO. What do you think?

https://github.com/keel-hq/keel/blob/5181df48108a0d86671ed5a2b35179d4918dc560/extension/notification/mail/mail.go#L75-L78