Maildrop not working
My Maildrop has stopped working on one Mac. It had been working for years, I upgraded computers but migrated data and kept the same OS (High Sierra) as my other devices.
The message I am getting is the standard "message too large for the server". I have checked all my settings against my other Macs which are working, and all is the same. Preference boxes are ticked to use maildrop on each of my email accounts within Mail prefs, both on gmail and iCloud addresses, and mail is active on the iCloud system pref settings.
I have tried dumping Mail prefs in the user library, reinstalling the OS completely (twice), and yet I still can't send. The file I am trying is a 32MB photos file which I have tried sending as a single zip file as well as full size individual photo files within a single email. I am nowhere near my limit in usage or file size. I sent the same file on another Mac with the same iCloud account and email address, and it worked fine.
After doing some reading, I tried a "postfix" stop start Terminal sequence to no avail. I can't find anything in the System Library that relates to this issue in Mail, and I don't see anything in the hidden var file that would help me. Everything else on the Mac is working fine. I have read forums, tried suggestions including unticking and re-ticking the accounts prefs "use mail drop for large attachments" option box. I have even tried to reset the mail drop file limit size using Terminal.
I also never get the "Would you like to send this attachment using Maildrop" message popping up.
Any suggestions as to how to reset this function in Mail or resolve this would be greatly appreciated.
iMac 27″, macOS 10.13