We just implemented Email-to-Case and we are facing this issue in our Salesforce Production environment.
When agents are replying to customers with email attachments, they emails are not being received by the customers.
We have not able to reproduce it in lower environments and everything was working in lower env from beginning - this was also tested thoroughly.
There are no access or other errors that they are getting.
They are able to attach the attachments from their system to the email they are about to send but still the customers are not receiving emails.
There are no errors in Salesforce. We still see the sent email with attachments.
Has anyone faced such an issue earlier / any possible resolutions?