mta_sts_dns_cname_max_depth

mta_sts_dns_cname_max_depth — specifies how many continuous CNAME lookups are allowed when doing DNS lookups for MTA-STS TXT record for a domain. Exceeding the configured value will be treated as a DNS lookup failure, which will be further treated as no MTA-STS policy available.

mta_sts_dns_cname_max_depth = 5

Momentum supports MTA-STS policy delegation, which points the _mta-sts TXT record for the policy domain via CNAME (to the _mta-sts record maintained by the provider). Momentum's DNS lookup will follow the CNAMEs. To avoid a DNS lookup loop, Momentum uses this config option to limit how many continuous CNAME lookups can happen before claiming a lookup failure.

The default value is 5.

mta_sts_dns_cname_max_depth is valid in the domain and global scopes.