Emails are not always being delivered

[Nick M.]

I know many of you are web developers and probably have run into similar issues.

Basically, some users are not receiving the emails I've sent them. These are not promotional or marketing emails. Rather, they are emails like account confirmation, password changes, etc. Importantly, it's happening to some but not all, and there doesn't seem to be a pattern.

Any ideas on how to solve the problem would help greatly.

Here are the details:

• WordPress site
• Tried using an SMTP server (MailGun) to solve the issue
  • Same issue with using the built-in wp_mail, SMTP server didn't help
• Checked the logs, emails claim to be delivered
• I've gotten reports from MSN and Gmail users
  • When I've tested with other Gmail accounts, it works
• Not on any blacklists
• SPF, DKIM, and DMARC records are set correctly
• Not in SPAM folders
• Marketing-style emails sent from MailCheat(Chimp) always work with these users
• It's happening to enough users that it's likely not a user-specific problem

More strangely, I cannot replicate the problem at all on my end. So whenever I find a "fix," I can't test it on my own.

Any ideas?

 

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[Pink Sheep]

Is it rare enough to be typos?
Special characters messing up anything?
Are there any roles/flags/groups in your back-end interfering?
If you check your server database, can you see any difference between a user that gets the mail vs someone who doesnt?

 

[Nick M.]

Is it rare enough to be typos?
Special characters messing up anything?
Are there any roles/flags/groups in your back-end interfering?
If you check your server database, can you see any difference between a user that gets the mail vs someone who doesnt?

My initial guess is that none of these are the case, but I will definitely look into all of them just in case.

 

[Ron Dee]

Can you access the WHM? If so, are these leaving the mail queue?

 

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[DaRK9]

What host?
Check for updates.

Test wp_mail function
Test PHP sendmail.

I had this issue and my host botched a PHP update.

 

[Nick M.]

Is it rare enough to be typos?
Special characters messing up anything?
Are there any roles/flags/groups in your back-end interfering?
If you check your server database, can you see any difference between a user that gets the mail vs someone who doesnt?

Ok, so far from what I can see, it shouldn't be any of these. And there doesn't seem to be a pattern between users or their email providers.

Can you access the WHM? If so, are these leaving the mail queue?

The emails are definitely leaving the queue.

What host?
Check for updates.

Test wp_mail function
Test PHP sendmail.

I had this issue and my host botched a PHP update.

Host is SiteGround.

Everything is up to date and wp_mail works on my end. Importantly, 90% of emails are getting through. Only around 10% are not.

Because of how I had the email setup, I could not check if the emails bounced or they simply weren't being delivered. Since yesterday, I've switched to SendGrid (since apparently delivery is better than MailGun) and have fixed the emails so I'll get notified if the emails are bouncing. This should either fix the problem or help gather data on where the issue is.