My Debian Exim 4.92 mailserver is configured to use the Backup MX service from dnsmadeeasy (208.80.120.10 & 208.80.120.11). Usually my mail server accepts emails from dnsmadeeasy but sometimes it rejects it with a "SPF check failed". What I am trying to figure out is why it is intermittent.
Here is an example of a successful mail delivery from dnsmadeeasy:
2022-09-17 12:32:19 1oZajl-0003EY-5e <= takagi064@sv5244.xserver.jp H=mx1.dnsmadeeasy.com [208.80.120.11] P=esmtps X=TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256 CV=no S=2146 id=TDYUaxswFpEVSsMltCQfVz84iIIbsuM0KJpXjs5Jsc@takagi064store.com
2022-09-17 12:32:19 1oZajl-0003EY-5e => joe <joe@domainhiddenforprivacyreasons.ca> R=local_user T=maildir_home
2022-09-17 12:32:19 1oZajl-0003EY-5e Completed
and here is an example where it is rejected for SPF check, but rejecting the exact same backup MX (208.80.120.11):
2022-09-16 14:42:47 H=mx1.dnsmadeeasy.com [208.80.120.11] X=TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256 CV=no F=<hydro-quebec@communications.hydro.qc.ca> rejected RCPT <joe@domainhiddenforprivacyreasons.ca>: SPF check failed.
I have noticed this problem occurs intermittently for both backup MXes I use. Can anyone here help figure out why this is happening?
(FYI - MTA is Exim 4.92 running on Debian 10 - Exim using split configuration files).
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