on reply email inbound action is not working instead of updating it is creating a new case.

[Yamsanibhavani]

Hi

Please help me out with the solutions you have.

Need steps to solve this.

Actually whenever we reply to the old case in the email subject line with case number, instead of updating the email, New Cases are being opened when replying to emails (sporadically).

Suggest me as many ways you have.

[Weird]

Does your reply email contain a configured reply prefix?
For example
"Test ticket INC0029345" might not be recognized as a reply

"re:Test ticket INC0029345" might be.

In Email properties the "Identify email as a reply by these subject prefixes" list the prefixes which might be "re:,aw:,r:,Accepted:,Tentative:,Declined:" oob.

If your prefix is not included there it might end up as a "New" email even if it has the ticket number. Safest bet for replies should be if the body contains the watermark of the ticket.

[Yamsanibhavani]

Thankyou so much for taking time to reply @Weird but I'm very new to ServiceNow, could you please guide me with steps, what to do and how to do if possible?

[Weird]

Take a look at the docs here:
Inbound email actions (servicenow.com)

The idea is that Servicenow reads the email and decides whether it's a forward, reply or a new email.
The prefixes can be found in navigation when you write "Email Properties" in it.
The properties have "Identify email as a reply by these subject prefixes" and "Identify email as a forward by these subject prefixes" which help Servicenow in recognizing replies and forward if other indicators are not found.

If your system is localized, then it might make sense to add prefixes in the local language as well.
For example in Finnish "re:" might be "vs:" instead.

So, based on the prefix you can try sending a test email to your test system for example.
First send an email where the subject contains an existing ticket number.

For example "This is a test on INC01923954" and check if it's recognized as "new" in servicenow. You can view received email in "sys_email" table.
Next try sending another email with the prefix in your Email properties.
For example I have "re:,aw:,r:,Accepted:,Tentative:,Declined:" on the property "Identify email as a reply by these subject prefixes", so if I instead send the email as "re:This is a test on INC01923954" it might instead be recongized as type "reply".

It's been a while since I've fiddled with these, but I'm sure the document page will give you great help.