Our Customer is using CRM 2015 on premise without an email router. Sometimes they experience an issue that a mail from CRM is resend every half hour. They see the mail in the send items in outlook.
Reconnecting the CRM plugin for outlook is not enough, they have to completely remove the mail from CRM to make it stop.
Without the emailrouter I don't know where to start looking for an issue or logfiles in CRM. Any ideas where I can find some information about the issue?