Hey Brian! :-) I did a quick test on this here by proposing new times for meetings from a variety of clients and server types, but I see the proposal/response in each case. Is there a specific client or server type involved in sending of the proposal?

Office365 and curanet.dk

I could send you one and we can test. Propose a new time instead of accepting.

Thanks Brian! I mean, is the sender on SmarterMail as well or are they sending from an Exchange server or other server type by chance? Often times when I see problems like this the critical piece is finding out the exact protocol being used, what server type the invite originates on, how it was created, etc. Thanks Brian!

I am sending it via outlook and SM.

Client is office365 responding. IDK if he is on outlook as well.

Thank you Brian, and apologies for the delay. And just to make sure we're on the same page; the client is also on SmarterMail or using something like Exchange?

Something like IMAP... https://www.onlinemail.io/ is the frontend.

But cant see the client itself.