Learn here how you can switch to a different e-mail extension.
Multiple e-mail extensions cannot be used at the same time.
If you activate the edit mode under Settings > Extensions > E-Mail by the respective existing extension, manually delete all input fields and finally save or click the "Connect now" button, then your current service is deactivated and you can change to another e-mail extension.
It is not possible for the previous service to continue working productively or send e-mails in the change-over period.
Due to the sending of the thank you e-mails, it is best to switch during a period when few online donations are expected.
Online URL: https://support.fundraisingbox.com/article/exchanging-e-mail-extensions-postmark-amazon-ses-private-smtp-server-379.html