Order confirmation emails with PDF not send

Hello,

I have configured my nopCommerce 4.40.4 store and had everything working as expected but was missing the Invoice in the emails to the customer.
When I added the PDF-invoice to some of the automated send emails like "payment complete", the emails that have a PDF in it return with an error :
smtp;554 5.6.1 Body type not supported by Remote Host

I was not able to find the source of this error so I tried to send emails through Office365 and MailerSend but with services I can not get them to send the emails. Testing from the Email configuration screen always throws an error. For Office 365 it could be due to the two factor authentication I have enabled and also tried the Office365 Exchange Connector, but no result.
Using MailerSend is giving a sort of equal response and can not connect to the server.
I already read several older posts on this forum about Office 365 and other email-send issues, but that has not resolved my issue.

Has anyone run into these issues also and how did you resolve it?

Did you turn on the Setting in
Order Settings > Pdf invoice
- Attach PDF invoice ("order placed" email)
- Attach PDF invoice ("order paid" email)
- Attach PDF invoice ("order completed" email)

Hi Andrew,

Yes, when I turned on the settings to attach the pdf’s to the email the emails with pdf attached are getting stuck in the queue

Check your email account credentials are working fine or not?
Also check by trigger Send Emails task scheduler.

RE: "... getting stuck in the queue"
Check the system log for any error messages.

Just an update on this. I resolved the issue. It seemed that the hosting provider of my VPS had a tiny little option checkbox in their dashboard outside of the firewall settings to open up outgoing mail ports.  🤦🏻‍♂️