Injects randomly fail to be sent when SMTP server refuse the connection too many times

[jborozco]

Description

Today we only retry 3 times when the connection fails.

Few idea on how to solve this issue have already been discussed internally:

1. Add more retry
2. Ping server & show that the server is not currently accessible during a short period of time.
3. Look for a new protocole

[RomuDeuxfois]

Solution chosen: Try an other SMTP provider

[RomuDeuxfois]

Discuss and seen on client side.

[richard-julien]

Reopen the issue. As the mailer produces random connection fail, we decides to try another provider. Ticket will be close depending of the result of this testing

[EllynBsc]

SMTP protocol was changed and after some monitoring, it seems to work properly so closing this issue. (cc @jborozco , @RomuDeuxfois)