Hice la siguiente prueba en este sitio https://mxtoolbox.com/diagnostic.aspx:
Prueba con smtp.gmail.com:
220 smtp.gmail.com ESMTP x7sm1194449qta.75 - gsmtp
Connecting to 173.194.205.108
220 smtp.gmail.com ESMTP x7sm1194449qta.75 - gsmtp [133 ms]
EHLO keeper-us-east-1c.mxtoolbox.com
250-smtp.gmail.com at your service, [18.205.72.90]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8 [122 ms]
MAIL FROM:<supertool@mxtoolboxsmtpdiag.com>
530 5.7.0 Must issue a STARTTLS command first. x7sm1194449qta.75 - gsmtp [121 ms]
RCPT TO:<test@mxtoolboxsmtpdiag.com>
530 5.7.0 Must issue a STARTTLS command first. x7sm1194449qta.75 - gsmtp [119 ms]
LookupServer 727ms
Prueba con ciunsa.unsa.edu.ar:
Unable to connect after 15 seconds.
Connecting to 170.210.200.2
2/22/2022 10:00:10 AM Connection attempt #1 - Unable to connect after 15 seconds. [15.03 sec]
LookupServer 15748ms
saludos.