Hi @ErikM9 ,
So, the three columns are Person columns, and you want to patch O365User to these columns (Append, not Update) and link their names to email, right?
First, If you use dropdown to select O365 user and save it to one of three Person Columns, Please apply the following codes to button OnSelect. I save the match record to variable, and append the selected user name to original person column:
Set(Var_Item, LookUp('Data source', 'Business Unit' = DropDown1.Selected.'Business Unit' && 'Site name' = DropDown2.Selected.'Site name' ) );
If(
AWS_Checkbox.Value, ClearCollect(SelectAWS,Var_Item.AWS); Patch(SelectAWS,Defaults(SelectAWS),{Claims:"i:0#.f|membership|" & UserDropDown.Selected.Mail ,Department:"",DisplayName:"",Email:"",JobTitle:"",Picture:""});
Patch('Data source',Var_Item,{AWS:SelectAWS}),
RBA_Checkbox.Value, ClearCollect(SelectRBA,Var_Item.RBA); Patch(SelectRBA,Defaults(SelectRBA),{Claims:"i:0#.f|membership|" & UserDropDown.Selected.Mail ,Department:"",DisplayName:"",Email:"",JobTitle:"",Picture:""});
Patch('Data source',Var_Item,{RBA:SelectRBA}),
3R_Checkbox.Value,ClearCollect(Select3R,Var_Item.3R); Patch(Select3R,Defaults(Select3R),{Claims:"i:0#.f|membership|" & UserDropDown.Selected.Mail ,Department:"",DisplayName:"",Email:"",JobTitle:"",Picture:""});
Patch('Data source',Var_Item,{3R:Select3R})
)
Then, let's talk about how to display the person column and click on the name to open Outlook to send an e-mail.
1. Add a MainGallery, and add a SubGallery in the MainGallery.
2. Set Items property of SubGallery to ThisItem.AWS
3. Set OnSelect property of SubGallery to Launch("mailto:" & ThisItem.Email)

Best regards,
Sik