Revert "Update INewsletterSender.cs"

This reverts commit f93305d1ea218b06b02068e75589c81713f5af7b.
Revert "Update INewsletterSender.cs"

This reverts commit de4d08530bf62bc5d19ac2bf57c5491916fd05bd.
Revert "Update and rename ISender.cs to ITransactionalSender.cs"

This reverts commit a84da52c14e9ac1f16772b529155a690be7a02e4.
Revert "Create INewsletterSender.cs"

This reverts commit 9b49b0fea76582415e5d421a78bf52027dff9610.