Cannot send large files via Mail Drop on Mail macOS Mojave 10.14.6
I'm sending an email with a PDF attachment from my iCloud account to another iCloud account. Mail says my message size is 22.5 MB, but when I try to send it I get:
"Your message has size 30.3 MB, which exceeds 28.3 MB, the maximum allowed by the server.
Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent."
(screen shots below)
In Mail | Preferences | Accounts | iCloud the option "Send large attachments with Mail Drop" is ticked.
Curiously, in the SMTP servers list there are two iCloud servers: "ICLOUD (offline)" and "iCloud" but when I click <Edit SMPT Server List> there is only one, "ICLOUD" but "In use by Account" is blank.
I've had no trouble sending large attachments from iCloud before. iCloud mail is otherwise working just fine.
Even stranger: in Mail | Preferences | Accounts | iCloud | Server Settings it shows "none". When I select either iCloud or ICLOUD from the drop down list, within a second it reverts to "none".