Relaying Denied by Sendmail

A family member reported she was no longer able to send email via a Sendmail service I have running on a CentOS Linux system. She sent me a screenshot of the message she received when attempting to send a message. I saw a "Server error: '550 5.7.1 ... Relaying denied'" message. At first, I thought that a technician from her Internet Service Provider (ISP) might have changed her Microsoft Outlook settings when he upgraded her network equipment recently, but then I remembered I was restricting email relaying on the system by IP address and realized her IP address would have changed when the technician upgraded her network equipment. So I had her visit whatismyipaddress.com and provide me with the public IPv4 IP address it showed for her. I then replaced her prior IP address in /etc/mail/access. The format for an entry to allow relaying from a particular IP address is as shown below.

You can include a comment to indicate who the IP address is associated with by prefixing the comment with a pound sign. The IP address should be followed by the word "RELAY" (you can put tabs in between the IP address and the word, if you like).

After changing the IP address, I rebuilt the access database with the makemap command. I then restarted Sendmail

I was then able to receive a test message she sent me. After updating the IP address, I may only have needed to restart Sendmail without running the makemap command first as I found the following at 19.3.2. Sendmail on a Red Hat website in reference to running the make all -C /etc/mail/ command (CentOS is derived from Red Hat Enterprise Linux):

All other generated files in /etc/mail (db files) will be regenerated if needed. The old makemap commands are still usable. The make command is automatically used whenever you start or restart the sendmail service.

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Renaming a PC and joining it to a Windows domain

If you need to rename a computer running the Windows 10 operating system and/or make it a member of a Windows domain, you can take the following steps. To see the system's current name, you can press the Windows key and the Pause/Break key on the keyboard simultaneously. Alternatively, you can type about in the "Type here to search" field at the bottom, left-hand side of the screen and then select the About your PC entry which is returned from the search. You can also type this pc in the "Type here to search" field at the bottom, left-hand side of the screen and then select the This PC app when you see it listed. For any of the three above options, you will then see an About window that lists "Device name," which is the system's current name. If you just need to rename the PC, click on Rename this PC. If you need to both rename the PC and join a Windows domain, then instead of clicking on Rename this PC, scroll downards in the About window until you see "Rename this PC (advanced)" and click on it.

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