Hi!

I need a simple answer to a simple question before I begin to configure sendmail (for the first time in my life by the way)
Can I use IP address instead of domain name? I hope if I know that it's not possible I'll save some time and efforts not trying to configure sendmail with IP address.

Thanks.

In theory, yes, but it depends what your goal is. If your goal is to simply get experience at configuring sendmail and testing if it works, then yes, it is technically possible to run it that way.

If your goal is to actually run a functional mail server on which you or others will depend for mail receipt, then probably not. At the root of things, if you are sending email from a domain literal (IP address) rather than a domain name, you will look like a spammer and mail will generally not be accepted by remote servers. Further, without an MX record, even more mail servers will fail to send you messages.

Finally, if you do not have a domain name, then chances are that your sendmail-reported hostname will not have a DNS record to look up and your IP address will not have a reverse DNS record pointing back to the sendmail-reported hostname. More rejection from remote mail servers.

Additionally, some ISP are known to restrict port 25 traffic, effectively disabling connections to any other mail server than their official mail server. And they may block port 25 so you cannot receive mail.