Email Delayed registration emails to gmail with specific domain

Hello everyone,

Question for the email gurus,

I have a few sites running on my server, all have a registration option and emails must be verified, thus, an email is sent out. This works perfectly with all email providers as far as I can see and through testing. Except one site, emails from this site work fine but only with gmail they are delayed for 5 min. When testing, literally delivered instantly to my zoho mail account, outlook account, and 4 other providers I tested. The strange thing is, the delay only hits the activation email, any other email triggered, such as forgot password, to a gmail account gets delivered immediately.

I know this is not a centmin issue, nor a server issue in general or else why would it work with every other provider.

I've verified my mx, and analyzed the headers on mxtoolbox.

I'm not sure if this has something to do with it and gmail doesn't like it, maybe,

My mx is zohomail but I use php mail to send out these sites' emails. I do have the servers email added to the spf line alongside zoho, and i have a dmarc line in addition to dkim signing.

I really don't know what gmail's issue is, and I filled out their contact form, but since this is google I'm not expecting a reply anytime soon, if ever.

Another hunch I have is maybe they don't like the content, maybe it's too generic or matches something they don't like, i don't know. The emails are ultimately never blocked and literally 5 min on the dot later they appear in the inbox, not even the spam folder.

Has anyone ever experienced or seen anything like this before.

 

I forgot to mention that in gmail, when the email is recvd, and I click on the verification email i was getting a "suspicious link" popup, "would you like to continue", this seems to have stopped as of today.

so im not sure if gmail doesnt like my one specific site, it's not blacklisted anywhere, same with the ip, that's clean, and i dont send out spam whatsoever and dont really have alot of emails being sent out, average over last month was just 32.

 

Thanks @eva2000, I was able to resolve this issue.

Everything checks out from the resources you published, and I believe this has something to do specifically with the content of the verification emails, for example the verification link is something like this: site.com/user/activate/UDFVMnJDUzUnJhREVndUVKMWJu?email=email@isp.com

and i had that url both in the link and out of it as the link itself

for ex. <a href=link from above">link from above</a>

this exposed link in text is triggering something on googles end, and once I switched it to <a href=link from above">click to activate</a>

then everything started working properly again, no delays or suspicious link popups.

So the moral of the story, don't use what i call exposed links in your email, as that seems to be bad for some reason. I'm sorry google for being transparent with people and showing them where theyre going with the link...