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Right now it seems that SmarterMail only does the reverse verification when doing reverse DNS checks, it does not do any forward confirmations either.
For example, mail server connects with IP 220.127.116.11 which resolves to mail.server.com, however mail.server.com resolves only to 18.104.22.168. To me this seems like an issue. Especially when many DNS providers will not setup RDNS entries unless the hostname is also forward confirmed.
IMO SmarterMail's RDNS checks should also perform forward lookup checks to make sure the entire cycle is completed.