DKIM and DMARC records

This is a quick guide to setup DKIM and DMARC records on your postfix-based ubuntu email server. I followed closely a guide from Julian Kunkel and am reproducing many steps from his post here. Despite the fact that he wrote his guide because he found some typos in other guides, his guide also had some.

I’ve been doing work on already working Ubuntu server (xenial, 16.04) with working postfix which I setup using that ArsTechnica article.

In the instructions I will use the placeholder <DOMAIN> for a full qualified domain such as You have to decide about a selector to use which basically provides means to use multiple keys, I use <SELECTOR> as placeholder, in my case, it is “mail”. <EMAIL> is an email where you like to receive errors (in case of DMARC).

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Upgrading of mail server

Today I added an additional volume to the mailserver prefect, since it was running out of disk space for the mailboxes. I have now increased the space by adding a new ‘virtual’ block storage, mounted and some mailboxes have been moved to the new drive. This new drive can be resized as needed with the lowest cost possible. We don’t need more CPU or memory, just more disk space and this works with $0.10/GB per month. The only drawback is that these volumes cannot be automatically backed up.

I have transfered the files from /var/mail/vmail to /mnt/vmail1/vmail by using rsync like this:

This transfered whole folders preserving all permissions and ownerships.