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[public-dns-discuss] Re: Intermittant DF Only from Gmail/G Suite

Hi Mark,

You wrote:
I'm the public DNS admin at TGH. Last Friday we started having trouble with some users at tgh.org being unable to receive mail from Gmail and G Suite users.
It appears that our MX record is resolving fine. I'm unsure where to look for more info on this. As a band-aid I increased the TTL on the MX records to 12H
in hopes that the entry would at least cache longer. This has resolved issues for most, but not all users. Some message are delayed several hours.

If there is a DNS issue, it concerns not just the MX record for tgh.org, but also the A records for your ProofPoint mail servers mx[ab]-00009101.gslb.pphosted.com. Those A records have rather short 30 second TTLs, and that could be an issue as well. 

But there are other potential causes of Delivery Failures than DNS. If there is a G Suite user who is experiencing problems, you could get them to send you a copy of a DF message they get when sending mail, and then try escalating through G Suite support. You might also want to contact ProofPoint support (if the problem is related to short TTLs for their A records, other users might have complained about this as well, and you could get them to increase that to a more reasonable 5 minutes).

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