GitLab MR Mail ID not Showing GitLab Self Hosted Server

Dear GitLab Team,

We have Self hosted GitLab Instance and we configured the incoming and reply by mails settings. Everything is working fine and Only Merge request mail ID is not showing after Migration Projects from another GitLab instance. Before Migration for Test Projects its shows MR Mail ID. Now also Email Issue is working ang only MR mail ID is not showing. Can you Please help on this