DKIM TXT Records Limits and Amazon’s Route53

Amazon’s Route53 has an unfortunate limitation on TXT records for DNS entries in that the TXT entry can only be 255 characters in length.

This becomes a problem when you try to use a 2048bit DKIM key for your domain. The Route53 service will give the error: *CharacterStringTooLong (Value is too long) encountered with ‘”v=DKIM1; k=rsa;*

The way to work around this is to break the TXT field up into parts, each 255 characters long. “Part 1” “Part 2”. So the DKIM key would have the first part in quotes ie “Part 1” then a single space/period and then “Part 2”.

The DNS system then sees the two TXT fields as a single TXT field and the DKIM TXT field is processed correctly.

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