Hi Jess,
Such issue can occur if several mailers use the same IMAP account.

An IMAP account should not be used by more than one mailer.

See the below documents which explain this:
Workflow Mailer Randomly Moves Response E-mail Notifications to the Discard Folder [ID 333444.1]
Unable to Connect to Mail Store in Workflow Notification Mailer Logs [ID 741352.1]

Extract of doc id 741352.1:
"You need to set a different account for each and every Workflow Mailer on same instance or different instances."

To check how IMAP account is set up on each environment, you'll need to run the below SQL on each of these environments:

SELECT b.component_name, c.parameter_name, a.parameter_value
FROM fnd_svc_comp_param_vals a,
fnd_svc_components b,
fnd_svc_comp_params_b c
WHERE b.component_id = a.component_id
AND b.component_type = c.component_type
AND c.parameter_id = a.parameter_id
AND c.encrypted_flag = 'N'
AND b.component_type = 'WF_MAILER'
AND c.parameter_name in('INBOUND_SERVER','ACCOUNT')
ORDER BY c.parameter_name;

Hope this will help,
Many thanks and best regards,

Isabelle

Usually, when we have a problem with an inbound email, the Workflow Mailer is deactivated. The DBAs have configured some kind of alert to notify them of this, but unfortunately I don't have any details about how this is configured. I'll see if I can find out any details. Is your Mailer being deactivated, or does it just stop processing?

I think the key would be to try to figure out why it is happening in the first place, so that you can prevent if from happening at all.

Do you see any clues in the log file? Any error messages?

Early on, we had some problems when people were responding through certain mobile devices. The device was automatically changing the NID to a phone number, which cause a problem when it came into the Workflow Mailer. I believe that there are certain settings you can do on the device to prevent this from happening.

We've also experienced errors when outside vendors send unsolicited emails where there is just a Subject Line and an Attachment, but no body.

Also, I don't believe you can have the Workflow Mailer account attached to Outlook at the same time it is processing. It can cause a lock, preventing processing. I would make sure that no one has the mailbox linked to their Outlook and I would also ensure that the email account is not used in another Instance, because that can cause problems as well.

If you can figure out the cause of the delay in processing, you might not need to configure an alert.