Issue SPF fail randomly

[seqoi]

I have terrible issue which i can not resolve.

Basically i have VPS, Plesk Web Pro, several subscribers, several domains.

What i am worried about is that some of my customers randomly get bounced undelivered emails.

But here is the problem. On online tools such as MX tools i am getting all green hits. On Newsletters spam test by mail-tester.com i am getting 9,5 out of 10 points. All green.

And i noticed when i send email from "troubled account" to my gmail sometimes when i look in gmail header i see all pass (dkim pass, dmarc pass, spf pass with ip from my server...all fine). - but randomly sometimes when i send from troubled account to gmail i see

SPF:FAIL with IP 2a01:4f8:xxx:xxx:x:x:x:x

That SPF issue out of 10 emails 4 will have this error on random occurrence.

SPF is just fine "v=spf1 +a +mx +a:domain.name -all
"

So basically my question is why does SPF fail sometimes, sometimes not?

 

[AYamshanov]

Hi seqoi,

If I faced the same issue, I would compare headers of two emails (delivered and bounced) and routes of delivery, IP-addresses, etc. Destination server makes a decision about pass or not SPF check. So, need to find what is different in headers.