У меня была такая же проблема, и я исправил эту проблему, изменив пароль на простой, чтобы просто проверить (без специальных символов).
Смотрите мой /etc/ssmtp/ssmtp.conf:
mailhub=smtp.zoho.com:587
# I use my domain. First you have to config the MX records
rewriteDomain=<your domain>.com.br
UseSTARTTLS=YES
UseTLS=YES
AuthUser=<your user>@zoho.com
AuthPass=<your pass>
AUTH LOGIN
FromLineOverride=YES
Смотрите мой /etc /ssmtp /realiases:
#You have to verify your domain on Zoho and create an email to use
root:<your email>@<your domain>.com.br:smtp.zoho.com:587
Смотрите здесь, как настроить записи MX
После этого вы можете проверить:
echo "Test message from Linux server using ssmtp" | sudo ssmtp -vvv dedeco@gmail.com
Результат:
[<-] 220 mx.zohomail.com SMTP Server ready September 27, 2016 8:09:04 PM PDT
[->] EHLO Shun
[<-] 250 SIZE 53477376
[->] STARTTLS
[<-] 220 Ready to start TLS.
[->] EHLO Shun
[<-] 250 SIZE 53477376
[->] AUTH LOGIN
[<-] 334 VXNlcm5hbWU6
[->] YW50b25pby5ldXN0YXF1aW9Aem9oby5jb20=
[<-] 334 UGFzc3dvcmQ6
[<-] 235 Authentication Successful
[->] MAIL FROM:<antonio.eustaquio@stratvision.com.br>
[<-] 250 Sender <antonio.eustaquio@stratvision.com.br> OK
[->] RCPT TO:<dedeco@gmail.com>
[<-] 250 Recipient <dedeco@gmail.com> OK
[->] DATA
[<-] 354 Ok Send data ending with <CRLF>.<CRLF>
[->] Received: by Shun (sSMTP sendmail emulation); Wed, 28 Sep 2016 03:09:04 +0000
[->] From: "root" <antonio.eustaquio@stratvision.com.br>
[->] Date: Wed, 28 Sep 2016 03:09:04 +0000
[->] Test message from Linux server using ssmtp
[->]
[->] .
[<-] 250 Message received
[->] QUIT
[<-] 221 mx.zohomail.com closing connection