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Sendmail and hostname config for another domain

au flag
Kalsan

The following example with fictional names describes my situation:

  • External mail service mailservice.com
  • DNS entry my.server.com points to the server publicly
  • The server should send e-mails from [email protected]

I'm struggling to understand how to name the server (hostname) and what sendmail config to use. Currently, I have the config:

# /etc/hostname
some-random-hostname-without-tld

# /etc/hosts
127.0.0.1   localhost some-random-hostname-without-tld my.server.com
127.0.1.1   some-random-hostname-without-tld

/etc/mail/sendmail.mc contains the minimal config for connecting to the account [email protected] on mailservice.com and defaults otherwise. DNS is setup correctly, i.e. MX, SPF etc. are in place to allow mailservice.com to send and receive mails as yetanotherdomain.com.

While sending e-mails works with this config, doing so takes over 60 seconds. /var/log/mail.info reports that:

  • Relay root@localhost reports immediately: "Message accepted for delivery"
  • Over a minute later, smtp.mailservice.com reports: "stat=Sent (Ok: queued as ...)"

The delay indicates that there is something with my config. As stated above, I'm unsure about which domain to use where. Thus, I have the following questions:

  • What do I need to assign to /etc/hosts as 127.0.0.1 resp. 127.0.1.1?
  • What should the contents of /etc/hostname be? Does it have to be something specific or can /etc/hosts make up for non-FQDN as hostname?
  • Do I need to configure a special host in /etc/mail/sendmail.mc or is use_cw_file good enough in my case?
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anx avatar
fr flag
anx
Try `openssl s_client -connect smtp.mailservice.example:25 -starttls smtp -crlf` and do the SMTP commands step by step (starting with `EHLO my.server.example`). It may well be your relay just being slow - or your relay failing to lookup your name or IP address and eventually giving up (I could have checked this if I knew the name.. which is why [you should not obfuscate by nature public names in your posts](https://meta.serverfault.com/questions/963/what-information-should-i-include-or-obfuscate-in-my-posts/6063#6063))
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anx avatar
fr flag
anx
Well, do `hostname -s` and `hostname -f` return expected short and fully-qualified names? What does the manual page for or the relevant section of your OS release notes say about how you should configure `/etc/hosts` (on many systems, you can bring it up using `man 5 hosts`)?
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au flag
Kalsan
@anx thank you for your answers. The latter helped me get `/etc/hosts` and `/etc/hostname` straight. `man hostname` contains a section "The FQDN" which documents how to set short and full domain name, namely `127.0.1.1 some-random-hostname-without-tld my.server.com`, which causes `hostname -s` and `-f` to work properly. The delay is still there, I will now probe manual connection via openssl.
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au flag
Kalsan
Turns out, the mail server does not support STARTTLS. Also, I replaced the `sendmail` setup by `msmtp-mta`, which made configuration significantly easier. Now, mails are sent and delivered instantly.
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