Send failed: “Could not instantiate mail function.”

It appears that it is more a question of who is sending from the mailing list.

Seems very strange to me…

Hi Michael / @mitfi

My guess is that your email provider (which may or may not be the same as your webhosting company) does not allow certain email headers to be set / overwritten.

Hence they are blocking your messages and you get that generic error message.

The most notorious one is the FROM email header where you may not be allowed to set the sender’s original address and may be stuck to using the mailing list address. And even for that setting: you mention using POST SMTP – be sure that you are using actual mailing list SMTP connection and not of some other of your email addresses.

Hope that helps.

Let me know how it goes!

Hi @brandtoss,

first of all: thanks for your time and your thoughts! Highly appreciated!

However, your assessments does not sound too logic to me (well, this might not be your fault ?? ), reason being:

1. My email provider is also the provider of my homepage (IONOS)
2. When some of my emails are part of a mailing list, everything works fine, sending from those
3. When others in the same mailing list send emails: worked fine in the past
4. When others send now (no setup change) it will fail with said error message
5. The error message is listed in the mailster archived email’s sending report, so it is detected by your plugin as if a class could not be instantiated
6. I am using wpmail for the mailinglist, not a specific SMTP setup, which worked well for a while
7. Trying to setup an SMTP server (IONOS) in mailster did never work out so far, whatever setting variant I try

I will now try to use the mailing list FROM address and see what happens…

Kind regards

Michael

Hi Michael.
The error “Could not instantiate mail function” is not really from WP Mailster.
If you put that into Google, you will get over a million results – about 99.999% not related to the plugin …

The message comes from the library PHPMailer that tries to send the email but cannot do so. Unfortunately, it is a very generic message.

Potential reasons include restrictions by your hoster. My first guess here was the FROM configuration.
If you say it is only sometimes happening, then my assumption would be that you send (sometimes) more emails per second/minute/hour than the hoster allows you to. Virtually all hosters have quotas, i.e. maximum allowed emails. Typically the hosters auto-block the account for a certain period of time before they can continue to send.
WP Mailster has therefore the option to enable send throttling to get around that.

You may sense a theme here: guessing.
If you want to find out what is what, ask the hoster for the reason. They should have logs about that.

The other thing to note is that most hosters typically enforce more restrictions if the standard mailer is used and not an authenticated SMTP connection.
Since you were not successful with SMTP: if you send me the credentials for a test email account via email ([email protected]), then I can help you with that.

Hope that helps.

Hi @brandtoss,

you were right!

I was always able to send mails (IONOS) to a mailiglist but a few colleagues weren‘t with said error arriving.

After selecting the maillist address as FROM address, leaving the FROM name as sender name via maillist: it appears to work. Thanks!

I will provide you now with the credentials of a test email account for SMTP check!

Thanks for your great and very kind support!

I learned a lot from this issue thanks to your help.

Kind regards

Michael

Happy to hear we figured it out.

For anyone curious: the IONOS configuration settings are now included in our mail provider settings list.