Renewed certificate, installed it but I can't decrypt my (new) Sent messages

OK, so my cert expired. I got a new one and installed it successfully and then tried sending out encrypted mails. The recipients are receiving them encrypted as normal and can read them fine. BUT…when I look in my sent folder, I cannot read them at all.

This is on Mac and iOS btw.

Thanks for your help (hopefully!)

I think its to do with Public keys…how would I retrieve my Public key again?