Set Submission port 587 for smtp out?

[ZenDevMaster]

Hi, thanks for this project! We've moved away from port 465 in favor of port 587 for all outbound SMTP client traffic, and eliminated POP3 too.

I was looking for a way to specify this confirmation, for example:

      IMAP_HOSTNAME: mail.server.com
      IMAP_PORT: 993
      IMAP_SOCKET: SSL
      #POP_HOSTNAME: mail.server.com
      SMTP_HOSTNAME: mail.server.com
      SMTP_PORT: 587
      SMTP_SOCKET: STARTTLS

But it does seem like the ports are statically configured in the templates. I also found that commenting out the POP_HOSTNAME will cause the server to fail to start. Perhaps that is a bad idea anyways, I'm not sure if email clients can still reliably parse the templates if POP info is missing.

I'm not a rust developer, but I'm guessing that extending the environment variable parsing and changing templates might not be too much of a challenge.

Starting somewhere around here for parsing:

mail-autodiscover-autoconfig/src/util.rs

Lines 35 to 45 in 2548f51

	let imap_hostname: String = env::var("IMAP_HOSTNAME").expect("IMAP_HOSTNAME must be set");
	let pop_hostname: String = env::var("POP_HOSTNAME").expect("IMAP_HOSTNAME must be set");
	let smtp_hostname: String = env::var("SMTP_HOSTNAME").expect("IMAP_HOSTNAME must be set");
	Config {
	domain: domain,
	display_name: domain.to_owned() + " Mail",
	imap_hostname: imap_hostname,
	pop_hostname: pop_hostname,
	smtp_hostname: smtp_hostname,
	}

And updating templates such as this:

mail-autodiscover-autoconfig/templates/xml/config-v1.1.xml.tera

Line 46 in 2548f51

<hostname>{{ smtp_hostname }}</hostname>

What do you think, is this a reasonable strategy or do you have any experience moving ports like this?