How to set Custom DKIM selector

How can i set custom DKIM selector other than ‘’ Custom DKIM selector should like ‘’

Thank you.


I also would like to know the answer to this. I have 2 mail-in-a-box servers running, let’s call mta1 and mta2. I would like to use mta2 (currently unused) via a lower priority MX record on in case of a critical failure in mta1
How can I change the DKIM selector for mta2 so that I can install a domain key TXT record for mta2.
Currently this seems to be hard coded to “mail” which means I cannot install the DKIM key for mta2 on - and no possibility of redundancy.
Any help much appreciated.