---> After I activate "Save"
Click "Save" in Dejaoffice?
Does that screen have message text / subject, passed there by AquaMail?
If it does, then AquaMail has done its part.
--> the message in Aqua appears: "Entry saved"
I would guess that's a message displayed by Dejaoffice, but it's a "Toast" and stays on the screen for a few seconds even when the app "behind it" (Dejaoffice) closes.
--> when I selecte "share" in AquaMail message view, some calendars appear (Google, etc.) but not DejaCalendar
Maybe you're supposed to "link" it to your Outlook first? Just a guess.
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To reiterate: if doing "Create calendar event" in AquaMail:
1 - Runs DejaOffice
2 - Passes through the message's subject and text
Then at that point, AquaMail has done its job and you're dealing with DejaOffice.