Watcher email action fails completely if there is at least one invalid email

[lucabelluccini]

Elasticsearch version: 6.2+ but can be applied to previous and latest versions

JVM version: not relevant

OS version: not relevant

Description of the problem including expected versus actual behavior:

In case we have several recipient emails in a email action, the watcher is NOT successful until ALL emails are valid.

Should we notify about the invalid format?
Should we notify about the failed delivery?

Steps to reproduce:

1. Install Elasticsearch and Kibana
2. Add email settings for watcher (a valid smtp)
3. Create a dummy watcher with an email notification and provide the several addresses as recipients
4. Test with recipients below

FYI the emails below are redacted:
xxxxxxxxx@gmail.com is a valid address.
yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy@gmail.com is a not existing address.
xxxxxxxxx+ahaha@gmail.com is a valid address (will be sent to xxxxxxxxx@gmail.com)

Several tests

xxxxxxxxx@gmail.com, gudsauigdsagiusadsadui, lol.com, a@com, xxxxxxxxx+ahaha@gmail.com, yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy@gmail.com

The watcher fails completely, no mail sent.

xxxxxxxxx@gmail.com, a@com, xxxxxxxxx+ahaha@gmail.com, yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy@gmail.com

The watcher is successful, all mails sent by SMTP. The SMTP Delivery service will notify later 2 out (a@com and yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy@gmail.com) of 4 emails cannot be delivered.

a@com, xxxxxxxxx+ahaha@gmail.com, yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy@gmail.com

The watcher is successful, all mails sent by SMTP. The SMTP Delivery service will notify later 2 out (a@com and yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy@gmail.com) of 3 emails cannot be delivered.

a@com, x

The watcher fails completely, no mail sent.

x, xxxxxxxxx@gmail.com

The watcher fails completely, no mail sent.

[elasticmachine]

Pinging @elastic/es-core-infra

[spinscale]

@lucabelluccini the correct solution to this would be to throw an error when putting the watch and any of those email addresses is not valid. Would that make sense?

[lucabelluccini]

Hello @spinscale, thank you for following this up.
Showing an error mentioning the email format would be more explicit for the user.

[spinscale]

I took a quick look into this, and all those email addresses are templateable - which means, they might be containing mustache templates instead of actual email adresses that are replaced on runtime. I opened #34042 - but I'd like to discuss this first.