We have 600+ subscribers and notification mails are bouncing hard. Most of them are blocked by server’s firewall.

550 relay not permitted (in reply to RCPT TO command)

SMTP error from remote mail server after end of data: 550 5.7.1 [TCR] Generating too many errors with receivers

I was told by the ISP that I need to slow down the sending rate. Is there any plugin for this? If bbPress Notify (No Spam) is the only one then I need to pay for the subscription for the Private Group Bridge add-on, which I would like to avoid since this site is non-profit and I am paying everything from my pocket. Hope there is another solution.

[@robin-w Moderator 5 years, 1 month ago]

did you try this?

AsynCRONous bbPress Subscriptions

[@madflute Participant 5 years, 1 month ago]

Yes, it has been installed but does not seem to help. The documentation suggests nothing about throttling, unfortunately.

[@robin-w Moderator 5 years, 1 month ago]

agreed, but many ISP’s stop emails with lots of bcc’s in them, clearly that is not your issue then.

[@madflute Participant 5 years, 1 month ago]

Yup. I actually consulted with our ISP and I was told to slow down the sending rate. Their firewall will blacklist me when more than 50 recipients a time and/or 1,000 emails in 1 hour.

[@robin-w Moderator 5 years, 1 month ago]

hmm…that’s awkward as would involve some custom code to fix, probably added to the above plugin.

I don’t have time to do this at the moment

[@madflute Participant 5 years, 1 month ago]

What’s interesting to me is that this issue doesn’t seem to be common. I found a few email throttle plugins but they are all 4-5 years old, untested, and abandoned. On the other hand, I thought this SMTP limiting was common practice to prevent from spamming. Very puzzling.

[@robin-w Moderator 5 years, 1 month ago]

most companies would send much more than 50 emails at a time, this limit seems very low, but yes most will block, many do it on bcc’s as these are the most used for spam.

[@gdragon Participant 5 years, 1 month ago]

My plugin GD Mail Queue: https://wordpress.org/plugins/gd-mail-queue/ solves the issue of BCC, and it can capture BCC emails and add them to the queue that is processed in the background as individual emails, so each notification is sent as a separate email, and it won’t get flagged by many email servers. The plugin has many more features, with the goal to replace other SMTP and mailing plugins. It has log, turning emails to HTML, email tests, SMTP configuration and more.