Mail doesn't send

Hi there,
I have a problem with the mail sending when an event is planning. It doesn't send the email. Here is fault after planning an event and suspect to send an email to the invited people. Van: Mail Delivery System <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Datum: 12 februari 2025 om 17:59:11 CET
Aan: Mail Delivery System <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Onderwerp: Onbestelbaar: Pronkzitting testThis is the mail system at host pmg02.zxcs.nl.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                  The mail system

<This email address is being protected from spambots. You need JavaScript enabled to view it.>: host
   gmail-smtp-in.l.google.com[142.250.102.26] said: 550-5.7.26 Your email has
   been blocked because the sender is unauthenticated. 550-5.7.26 Gmail
   requires all senders to authenticate with either SPF or DKIM. 550-5.7.26
   550-5.7.26  Authentication results: 550-5.7.26  DKIM = did not pass
   550-5.7.26  SPF [hotmail.com] with ip: [185.104.30.187] = did not pass
   550-5.7.26  550-5.7.26  For instructions on setting up authentication, go
   to 550 5.7.26   support.google.com/mail/answer/81126#authentication
   a640c23a62f3a-ab7ea47ea97si220839366b.591 - gsmtp (in reply to end of DATA
   command)

Hi, I can't reproduce your issue. Please give more informations about your system Joomla, JEM, PHP.
For me it seems more a Joomla than a JEM problem.
The mail test at the end in Joomla > configuration > Server is working?
And there are other tabs in the JEM-mailer settings, not only the first tab "plugin", which are relevant.
 

The return mail say:
550-5.7.26 Your email has been blocked because the sender is unauthenticated.

Your Joomla is sending email by Gmail, but you don't have credential in your Joomla setting. Review Global Configuration - Server - Mail these fields:
- SMTP Authentication
- SMTP username
- SMTP password
It's better to send email from your email server (service) and if your domain has STP active, review the TXT register.
This isn't JEM error.