An SMTP server that never sends its greeting makes an email send hang #2039

pkg/mailer sends through gopkg.in/mail.v2 v2.3.1. Its Dialer.Dial reads the server greeting (smtp.go:91) before it sets the connection deadline (smtp.go:96-98). If the SMTP server accepts the connection but never sends its greeting, the send blocks with no deadline.

Every email goes through this path: the login OTP (core/authenticate/strategy/mail_otp.go:95) and magic link (core/authenticate/strategy/mail_link.go:75), invitations (core/invitation/service.go:222), PAT alerts (core/userpat/alert_service.go:244), and the organization delete email (core/deleter/delete_notice.go:249). #2034 adds the user delete email on the same path. Most of these send inside a request, so the request blocks with the send.

It needs a mail server that accepts the connection and then stays silent, so it is rare.

Possible fixes:

• Set the deadline right after the connection opens. The library exposes its dial as mail.NetDialTimeout (smtp.go:77), so pkg/mailer can wrap it once at startup.
• Move to an SMTP library whose send takes a context.