Hi John,
I assume you are using the ADD_ATT script, right? Before V11 it was possible to separate email addresses via colon or semicolon, but that doesn't work anymore.
You can do one thing though, use the :WHILE "command" for your requirement.
Example:
:SET &MAILADRESSES# = GET_VAR(MAIL.VARA,RECIPIENTLIST)
:DEFINE &RECIPIENT#,string, 10
:FILL &RECIPIENT#[] = STR_SPLIT(&MAILADRESSES#,",")
:SET &LENGTH# = LENGTH(&RECIPIENT#[],SIZE)
:PRINT &LENGTH#
:SET &COUNTER# = "1"
:WHILE &COUNTER# <= &LENGTH#
:ADD_ATT RECIPIENT, "&RECIPIENT#[&COUNTER#]"
: SET &COUNTER# = &COUNTER# +1
:ENDWHILE
Regards
Jan