FAQ on Email delivery

[crythias]

Why am I not being able to send email/notifications/autoreplies?

Things to check:
for customers:
Auto responses aren't assigned to queues.
Customer Preferences is "no"

for agents:
Agent notification preferences are "No"
Agents don't have a specific queue selected in "My Queues"
Agents don't have a good email address.

email travel:
Inability (errors) to send:
SMTP authentication invalid.
Sending as an email that isn't allowed to send via SMTP configuration.
Check Queue System Address (Queue),
Notification Sender (SysConfig), and your SMTP relay.

Turn off MX checking in SysConfig.

email receive:
"Empty" email - something else is also popping/retrieving emails .. either your dev box or another mail device.

Stuck mail message too big, keeps attempting to dl/fails:
Use another email client to delete the message or attachment.

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This is a rough draft, but since it seems to be asked a lot, it'll be updated here.