How do notifications work internally?

[Mikel WHIPPLE]

I am seeing some interesting behavior, and I am not sure where to see how notifications are firing.  For instance, if I have a notification set to notify assignee and group field for the "you're assigned a work item", if there is no assignee will it notify everyone in the group? If there is an assignee and a group, will it notify both? What if I am in the group and change it to my group, will it notify me and the group or just the rest of the group, or none of us? Also, where can I see all the outgoing emails at? I am seeing some team members notified, and some not and they are very much in that group. Thanks. 

[Evgenii]

Hi, @Mikel WHIPPLE 

Q: I have a notification set to notify assignee and group field for the "you're assigned a work item", if there is no assignee will it notify everyone in the group?
A: Yes, it will notify the group. Notification will be sent to everyone who you added in the Notification scheme for that scenario, as long as they have Browse Projects permission on the issue.

Q: If there is an assignee and a group, will it notify both?
A: Yes, both will be notified. Notification will be sent to everyone who you added in the Notification scheme for that scenario. If a user matches both entries (assignee and group member), Jira deduplicates and sends only one email.

Q: What if I am in the group and change it to my group, will it notify me and the group or just the rest of the group, or none of us?
A: The rest of the group will be notified, but you will be skipped by default. Jira Cloud doesn't notify you about your own changes unless you enable the option "You make changes" in Personal settings > Email notifications for issue activity.

Q: Also, where can I see all the outgoing emails at? I am seeing some team members notified, and some not and they are very much in that group.
A: I'm afraid it's not possible. Cloud instance doesn't offer an outgoing email log, only Atlassian Support can check actual delivery on their side. But you can use Notification Helper (Settings > System > Notification helper) to check whether a specific user would receive a notification for a specific issue and event, and why not. Most common reasons for "in the group but not notified" are missing Browse permission, personal notification preferences, or the user being the one who made the change.

Also, it's worth to look at 
https://your-company.atlassian.net/jira/settings/personal/notifications
There user can configure, what he want/don't want to receive. It overrides system settings.