Most museums have more artefacts than they can ever display and your gift, while thoughtful intended, become more of a burden. A donation also takes the material out of the hands of philatelists who could use the key item in an exhibit. Harmers has a win-win solution.
You would like to put your collection in the hands of an institution that will share your items with generations of philatelists.
The museum's reality
The museums often have more items than they need. Your gift must be maintained and stored. If your gift permits selling, they may sell items, but restrictive gifts may sit in storage for decades.
The Harmer Solution
Harmers would like to see a program where the material is loaned to collectors to use in their exhibits at an appropriate fee with insurance and the covenant that when the Museum would like to display the item that it is made available. This would keep the item in circulation and generate revenue for the museum.
Harmes can not control the museums, but they can offer your items for sale subject to exhibition clauses or use rights for a museum of your choice.