I’ve created a little AppleScript that copies the mail contents and attachments into an OmniFocus task. It also creates a back-link into the OF task, and a forward link as a MailTags note.
(* Create an OmniFocus task in the OF Inbox from Mail that has a link back to the eMail, such as message://%[email protected]%3e -- (c) 2018 Matthias Nott *) use AppleScript version "2.4" -- Yosemite (10.10) or later use scripting additions -- -- Configuration -- property assignedKeywords : {"#todo"} -- Tag to set property quickEntry : false -- use Quick Entry -- -- Main Program -- on run set crt to ASCII character 13 tell application "Mail" set theMessage to "" set theInboxMessages to selection if (count of theInboxMessages) is greater than 0 then repeat with theMessage in theInboxMessages set theSender to sender of theMessage as string set theSubject to subject of theMessage as string set theTitle to theSender & " — " & theSubject set theURL to ("message://%3c" & message id of ¬ theMessage & "%3e" & crt & crt) as rich text set theNote to theURL set theNote to (theNote & content of theMessage) set theAttachments to "" set theAttachmentsCount to count of ¬ mail attachment of theMessage if theAttachmentsCount is greater than 0 then set theMailAttachments to ¬ mail attachments of theMessage repeat with theMailAttachment in theMailAttachments set theAttachments to theAttachments & ¬ name of theMailAttachment & crt end repeat set theNote to ¬ theNote & crt & crt & "Attachments:" & ¬ crt & theAttachments end if set theTaskID to my makeOmniFocusTask(theTitle, theNote, quickEntry) -- set background color of theMessage to purple if (quickEntry is not true) then using terms from application "MailTagsHelper" set keywords of theMessage to assignedKeywords set note of theMessage to theTaskID end using terms from end if set flag index of theMessage to 5 set read status of theMessage to true end repeat end if end tell end run -- -- Make an OmniFocus Task -- on makeOmniFocusTask(theTitle, theNote, isQuick) tell application "OmniFocus" if (isQuick = true) then tell quick entry set theTask to make new inbox task with properties ¬ {name:theTitle, note:theNote} open end tell else tell default document set theTask to make new inbox task with properties ¬ {name:theTitle, note:theNote} end tell end if end tell set theTaskID to "omnifocus:///task/" & id of theTask return theTaskID end makeOmniFocusTask