It is known that enabling TLS affects the mailing speed in LM especially when there are a large number of TLS enabled domains in a mailing list. You may want to know if it is possible to disable TLS for specific domains in a mailing list in order to improve the mailing speed in LM.
Once TLS is enabled in the configuration file, it will be enabled for the List Manager instance. TLS cannot be disabled for specific domains in a mailing list.
Some recommendations for improving TLS performance are given in the following article: