This article covers 

What happens when my SMTP server is having downtime issues?

Summary

When your SMTP servers have downtime issues, Chargebee keeps them on hold and re-try the email triggers after some time. 

Chargebee’s smart mechanism triggers multiple email attempts if the downtime continues for long. If multiple re-attempt fails then, Chargebee sends out a notification that reads, 

“This is to inform you that one or more notification email(s) could not be delivered to the intended recipient(s) even after several retry attempts”

You can take necessary actions at your end based on our inputs (Error Logs between our server and your SMTP).

Related articles and Documentation

How can I use a custom SMTP for our email notifications from Chargebee?

Error - Less secure app, when setting up smtp.gmail.com