Hey Ali,
The Create new mail message action only allows 1 file attachment.
If you need to attach more than 1 file you’re probably going to have to resort to AppleScript.
Here’s an example:
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# Auth: Christopher Stone
# dCre: 2013/05/15 06:11
# dMod: 2016/02/04 23:46
# Appl: Apple Mail
# Task: Make a new outgoing message.
# Libs: None
# Osax: None
# Tags: @Applescript, @Mail, @Make, @New, @Outgoing, @Message
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set attachmentList to {alias "Mercury:Users:someone:Documents:Keyboard Maestro Stuff:Exported Macros:ACME Telephone Number Look-Up.kmmacros", alias "Mercury:Users:someone:Documents:Keyboard Maestro Stuff:Exported Macros:FrogScript.kmmacros"}
set toName to "Robert A. Heinlein"
set toAddress to "bob@pieinthesky.com"
set _sender to "H. Beam Piper <beam@littlefuzzy.org>"
set _subject to "Test Message"
set _body to "Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal."
tell application "Mail"
set _msg to make new outgoing message with properties {subject:_subject, content:_body & return & return}
tell _msg
set visible to true
make new to recipient at end of to recipients with properties {name:toName, address:toAddress}
set sender to _sender
repeat with theAttachment in attachmentList
make new attachment with properties {file name:theAttachment} at after the last paragraph
end repeat
end tell
activate
end tell
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-Chris