Given that 'Date of service' is in column 'A' and 'Date of mailing' is
in column 'E'.

Add the formula =TODAY()-365 to cell G2

add the formula =AND($A2<$G2,$E2<$G$2) to cell F2

Drag the formula in F2 down as far as required.

'TRUE' will be displayed when a reminder is needed - e.g when BOTH the
service and mailing dates are a year old.

Hope this helps

Kev