If we generalize a bit I understand you are asking if expenses related to tzedakah count as tzedakah, with a subcase being when expenses are for the convenience of the donor.
Eretz Hemda addresses a very similar scenario
For sure, the full amount [you spend which] counts. It is rare to give donations where
there are not costs in some form and usually there is no way to avoid
or to calculate how much.
In general, it is how much you spend on it.
For example, you can count toward maaser the stamp and envelope (if
you still send that way), even if I don't know I would suggest being
R Shimon Taub in The laws of tzedakah and maaser (p. 104) says a charity collector is permitted to deduct from the tzedakah account any expenses that were incurred to enable the tzedakah fund to function. I think the analogy holds here as well.