Make hostname in SMTP ehlo configurable

I'm actually not quite sure what the best behavior would be. I've tried to follow the standards, but I'm not sure it really does any good to use a meaningful IP address in the EHLO anymore. Especially not when most SMTP servers already require authentication before allowing a user to send messages.

For now I've added the following hidden preference (untested though):

defaults write com.freron.MailMate MmSMTPFixedIP -string "127.0.0.1"

Note that [] should not be included.

I've closed the ticket, but if anyone has an opinion (references) on the subject of default behavior then they are welcome.

[bulk edit]

RFC5321 and its recent ancestors allow [bracketed] IP literals in EHLO/HELO arguments when a client hostname that would be correctly meaningful to the server is unknown, but there's a clear preference for a name over an IP literal in the RFCs. Operationally, there are some mail severs which treat mail with greater distrust when it is offered on a session with an IP literal HELO argument because empirically the only SMTP clients that use IP literals are MUAs like MailMate (which usually mitigate the issue by authenticating) and spambots. While the most common use cases for MailMate do make an IP literal the best choice, it would be helpful to support the use of a proper hostname, either by allowing the user to set it explicitly with a special preference like MmSMTPFixedIP and/or by detecting when the system has a reasonable FQDN configured as its hostname, e.g. a name which doesn't end in an invalid or reserved TLD (e.g. .local, .test, etc) and resolves to an IP address that either matches an IP on a network interface OR is a public IP while the machine's network interfaces only have RFC1918 addresses (i.e. is likely to be the name of a NAT address.)

Maybe my last comment was too verbose, as it didn't spur any response.

Short form: It would be helpful to be able to set the HELO argument to a hostname because that is both the formally preferred behavior AND it can allow a single setting to be correct across all accounts, even when network circumstances make the client appear at different IPs to different outbound servers.

The simplest way to do this would be to detect whether MmSMTPFixedIP is an IP address or a hostname, and if it's not an IP, skip putting the [] around it.