I have the same problem with email notification in 2860 in December 2024. I tested PlainText, SSL and StartTLS settings. I also used SMTP DNS server name or IP address. Still the same, nothing sent.....
In syslog only this appears:

 2024-12-01 22:44:24     [WEB]Send test mail.
 2024-12-01 22:44:23     [WEB]Send test mail.
 2024-12-01 22:44:22     [WEB]Send test mail.

I must add that I am using: Firmware Version 3.9.8.3_VT5

I have a Vigor 2860, running firmware 3.9.8.3_BT, and mail alerts seem to send OK, through my SMTP2GO relay. I have some screenshots of the config, in case it helps, but i can't figure out how to attach images here .

Interestingly, there seem to be two places one can configure mail alerts: Object Setting > SMS/Mail Service Object (Which is then referenced by a Notification Object), and System Maintenance > Syslog / Mail Alert. I think I have it setup in both places, and both are working OK. (One sends notifications for DoS attacks, the other for WAN Offline alerts). 

Since enabling this, I have been mystified by certain log messages (See  this forum thread ) however the mail alerts themselves are working fine.

 

I assure you that I have tested both:
System Maintenance >> SysLog / Mail Alert Setup
and
Objects Setting >> SMS / Mail Service Object
neither of them works... ;(

in addition, I don't know why You use SMTP2GO relay. That's what the Authentication field is for, so you have to check it, enter your login and password for your email account to send emails so as not to use SMTP Relay..... besides, from what I know, most email servers block relaying emails.

Well, I am using SMTP2GO because I already have an account for other purposes. 

That's what the Authentication field is for, so you have to check it, enter your login and password for your email account to send emails so as not to use SMTP Relay..... besides, from what I know, most email servers block relaying emails.

Indeed, hence I have added my SMTP2GO SMTP credentials in the authentication field. Sure, I could set it up to use my own SMTP server for instance, or perhaps a personal email account (E.G Gmail), but I am using SMTP2GO to send emails from an alerts@ address on my own domain.

One thing to check is what authentication your email servers support. I'm not sure about Zoho, but some email providers have disabled basic authentication, requiring instead the likes of OAuth, which the Draytek doesn't support. 

besides, from what I know, most email servers block relaying emails.

Correct, any properly setup mail server these days should absolutely block unauthenticated relaying. However, SMTP2GO is a dedicated relay service, and besides, I am using authenticated SMTP, not open relay.

I have to agree with you on this, I also think, that the problem is in the version of the SSL or even TLS protocol being used.
https://www.wolfssl.com/docs/ssltls-protocol-comparisons/

You mentioned trying PlainText. Are you 100% sure that PlainText does NOT work? (Check your email provider actually supports non-encrypted connections).

I do vaguely remember something strange about this not working initially until I tried changing the username or password or something, so perhaps do as 'mbames' says for a test - short user & pass for the mail server.