Hi @JAY_dev :
Do you want to collect the email addresses selected by the gallery and send messages to these email addresses?
I suggest that the Concat function connect the selected addresses with ";" so that you can send multiple emails at once.
I'v made a test for your reference:
1\My data source:
ClearCollect(TheMail,{mail:"XX@XXXXXX.com"},{mail:"bof@XXXXXXXX.com"},{mail:"46XXX71@qXXX.com"},{mail:"XXXng@XXXXXt.com"}) /*TheMail is my custom collection*/
2\Add a gellry
Items
TheMail
3\Add an arrow into this gallery
OnSelect
Collect(waitforsent,{mail:ThisItem.mail}) /*waitforsent is my custom collection*/
4\Add a lable(Used to show the result of the concat function, you can skip this step)
Text:
Concat(waitforsent,mail,";")
5\Add a button (you should add an office365outlook connection first)
OnSelect
Office365Outlook.SendEmailV2(Concat(waitforsent,mail,";"),"Subject","Body");Clear(waitforsent)

I think this link will help you a lot
Send an email (V2)
Best Regards,
Bof