Yes, I guessed they couldn''t know who it was from. They also have not responded to my email.
There are other strange things such as sending me a letter without the name of the solicitor representing my stbx and on the same letter it was hand signed with the name of the company rather than the person who sent the letter. Why would they be doing these strange things?
I was advised in connection with a completely unrelated matter that normal 1st class post with a certificate of posting would be accepted as proof of delivery and that to be absolutely sure it was a good idea to send three copies from different post offices all with certs of posting.