Split regex not handling '^' and '$' metacharacters at mail handler

When trying to remove mail signatures beginning with - from comments, putting split regex with -$\ or ^-\ does not catch the signature mark

(-)

Steps to Reproduce:
Create mail handler with type "Add a comment before a specified marker or separator in the email body" with split regex = /^/ or /$/

Expected Results:
JIRA should remove all text following the - beginning a line on the message content
e.g.:

This is the message content
-
Marcus Silveira
Atlassian Support

JIRA should add 'This is the message content' as a comment.

Actual Results:
JIRA adds the whole message, with the signature.