follow the steps below:
Step 1. Get DKIM keys length
Verify the domain’s DKIM key length and write them down if it’s using a 1024- or 2048-bit key length
In this example, selector 1 has a 1024-bit DKIM key.
and Selector 2 has a 2048-bit DKIM key.
You want to have all DKIM keys set as 2048-bit keys.
Find all the domains and their DKIM key size
To get all the information for a single domain.
Upgrade DKIM key to 2048-bit for the domain.
Note: Upgrading the key size to 2048 only upgrades the selector that isn’t currently active. After key rotation has taken place, you need to run the command again to upgrade the key size of the other selector. But that’s only possible after 4 days.
Verify that the 2048-bit key is set for the domain.
The output shows the 2048-bit key.