As far as the “Sent as SMS via server” message goes, you should know it’s commonly received when the recipient has an IOS device that does not yet support RCS or an older Android phone. In some cases, the message may be sent if the recipient has disabled RCS on their device. Whatever the case, there’s no reason to worry if you do receive a “Sent as SMS via server” notification since it merely serves as confirmation that your message was, in fact, sent, just in a different way. Likewise, there’s no reason to believe the message or media sent was altered in any way.
Since the notification is not an error message or a sign of some system failure, there’s no real reason to take action upon receiving one. However, if you’d rather not receive them, you can turn off the notifications on your Android device. You can also turn RCS off altogether if you so desire. However, turning RCS off is not generally recommended since the text messages you send may not be end-to-end encrypted without it. On top of that, any multimedia accompaniments you send will consume more mobile data.
By most estimations, the “Sent as SMS via server” discourse is a case of much ado about nothing. Still, it may comfort Android users to know the messages are no big deal and that they can opt out of receiving them if they like.