When sending emails to the default mail handler of a JSM project with a "\" on the summary, some mail providers replace it by "\r\n" and it causes errors to create tickets:

Your request could not be created. Please check the fields have been correctly filled in. Please provide a valid value for field 'Summary'

There's no pattern which can be formed. There are also some cases which passed with one provider (Microsoft) and failed with other (Gmail) and vice versa.

For eg: below subject will fail when sent from outlook, but will pass if sent from Gmail:

Qttttt543xxxxxaaaaaaaaabbbbaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa:\ bbbbbba

The workaround is to avoid sending emails that contain "\" on the summary.