By wizzle - October 25, 2017

I've been having this problem since just after launching the website back in July (3 months) but have been too busy to really address it...

The website is an organization of homeschool families in a local area.  Families join the organization through the website.  I am using the website membership plugin with CMSB to accomplish this. 

Aside from the nearly static information on the website, there are 2 basic features that are used...

1. A membership forum using the forums plugin.
2. The organization's board members can post events and announcements directly to the website (using CMSB). In addition to the new events and announcements posting to the website, an email with the new event or announcement is also sent out to the members.

Here's the issue I'm having...

There are several member's for whom the emails are getting rejected by their email service provider and bounced back to me as Undelivered Mail Returned to Sender.  The emails getting rejected are from forums and event/announcements.

I have verified that the email are actually being sent and that is the recipient email provider that is rejecting them. Unfortunately it doesn't seem to be a single email provider... I have rejected emails that are hotmail, aol, microsoft, yahoo, and I think Gmail.  But I have other users with those same email services who DO get the email.

The bounceback "undelivered Mail Returned to Sender" messages include something like


<email address>: delivery temporarily suspended: host[] refused to talk to me: 421 4.7.1 :

Final-Recipient: rfc822;
Original-Recipient: rfc822;
Action: failed
Status: 4.7.1
Diagnostic-Code: X-Postfix; delivery temporarily suspended: host[] refused to talk to me: 421 4.7.1 :


There are about 150 members, and about 8-10 who's emails get returned to me as undelivered.

I have tried working with my hosting company but they seem sluggish on this issue.

It feels like the emails are getting tagged as spam or something and not being allowed to pass through, but I have no idea how to address that.


By jenolan - October 25, 2017

I always use Sendgrid to actually handle sending, it is free for small sites so it is worth using. They do all the work adding the headers required to get past most SPAM/WhiteListing services.



By Dave - October 25, 2017

Hi Larry, 

The linked AOL error indicates: 421 DYN:T1

  • The IP address you are sending from has been temporarily rate limited because it is not Whitelisted, unexpected increase in volume, or poor IP reputation.

How many @aol emails are on your list?  I found some info on AOL's rate limits here:

It may be that your SMTP provider is sending more messages per connection than AOL allows, or that the sending server IP is blacklisted.  You could check here:

Hope that helps!

Dave Edis - Senior Developer

By jenolan - October 25, 2017

Not me, I use SendGrid ... :-)


By Dave - October 25, 2017

And by "Larry", I mean "Wizzle". lol :-)

Dave Edis - Senior Developer

By wizzle - October 25, 2017

It also just dawned on me that cmsb already has the swiftmailer 3rdParty app included, which I believe is similar to the referenced phpMailer.  

Could I just modify the sending code to utilize swiftmailer instead of the built in php mail() function? 

If that's possible, it seems like that would have already been done in the forum plugin.  Am I missing something?

By Dave - October 26, 2017

Hi Wizzle, 

Yes, for any CMSB code or plugins you can change how mail is sent under: 
Admin > Email Settings > How to send mail (and selecting SMTP)

However, if the issue is that your web host's mail server IP's are being blocked then you'll have the same issue and the solution would be to use a 3rd party mail sending service.  Hope that helps!

Dave Edis - Senior Developer

By wizzle - October 26, 2017

Thanks Dave.  I'll give it a shot.

One question.

I was under the impression that I would need to find all the instances where the php mail() function was used and somehow change it within the code to mail using smtp instead...

but it seems from your suggestion that I don't need to change anything in the actual cmsb or plugins files, and that I only need to change the "How to Send Mail" selection in the Admin>Email Settings.

Am I reading that right?  I should only change the settings but don't have to actually change the mail() function within the code itself? 

By Dave - October 26, 2017

Hi Wizzle, 

Yes, that's right.  You only need to update mail() calls in custom code you may have created yourself.  For all our code we call our own function called sendMessage() that uses the CMSB mail settings, can log outgoing mail, etc. 

Dave Edis - Senior Developer