ServiceNow stopped updating additional comment from Guest replied Email

[bbf35621]

Hello devs,

Last Friday, I set up a Case updated comment notification that sends out to the watch list, consumer, and is assigned to. I added my personal email to the watch list, which is a guest. Whoever made a comment in an additional comment, I got that notification in my personal email. Then I reply to that notification and the ServiceNow case updates my reply in the additional comment case ticket. Everything looks good until I test it again yesterday and today, ServiceNow has stopped updating additional comments from the Guest replied email. Currently, it only works for SN users. Does anyone know why that happened and where I should troubleshoot? I haven't changed anything, and I have tried adding ACL write in the Case comment to allow Guest, but it is not working.

Here is a sample screenshot of the last time it was working,

[Nawal Singh]

Hi @bbf35621 ,

Here is the few things that you need to check and fix -

1. Check ACLs on Comment Fields

Go to System Security → Access Control (ACL)

Locate ACLs for fields like comments, work_notes, or additional_comments

Ensure Guest user or external users have write access if needed

Add an ACL with a script to allow Guest

2. Review Inbound Email Actions

Go to System Policy → Inbound Email Actions

Locate the action used for replies or comment updates

Verify the conditions (like “from recognized user”) don’t block guests

Ensure the script doesn’t skip execution for Guest or unknown users

Make sure no higher-priority action is blocking it

3. Verify Guest User 

Check if the external email address maps to a user in sys_user

If it’s not mapped, the system uses the Guest user account

Make sure the Guest user has required permissions

4. Analyze Email Logs

Go to System Logs → Emails (sys_email)

Find the incoming reply email

Check if it was received and processed, or skipped

Look for errors like “No matching user” or “Action skipped: condition not met”

If my response is helpful please mark as helpful and accept the solution

Thank you!!

[bbf35621]

Thank you for providing options to check.

At #4, I found an email log that skipped it and an Error string,

and

It said it was unable to find the sys ID of the case, but we have an active case sys ID that matched this sys ID. I have been replying to the same case from last Friday, and now it seems not to be recognizing it.

I checked the successful log and it found that same case, 

Do you know why?

[Ankur Bawiskar]

@bbf35621 

the user who is replying should have write access to that record and also the comments field

Did you check that user is satisfying these ACLs?

Any recently added ACL is blocking?

If my response helped please mark it correct and close the thread so that it benefits future readers.

[bbf35621]

There is no ACL block. I have replied to other of my findings below. The result is that it was unable to locate the Case sys ID with sys ID to append the reply to the additional comment. However, that case sys ID does exist, and it is the same one that I tested last Friday. I am not sure why.