Pro literally means "because of", so "Dankon pro vi skibis al mi" = "Thanks because of you wrote to me".

"Dankon pro via letero/mesagxo/skribo/skribado" is fine though, because it's a noun phrase and not a verb phrase.

ceigered:"Dankon pro via letero/mesagxo/skribo/skribado" is fine though, because it's a noun phrase and not a verb phrase.

Somehow, 'skribo' and 'skribado' sound a bit weird in this context. I mean, we're talking about a letter or an email, so it's best to use the more relevant words:

letter = letero
mesagxo = message

If we're talking about an email, then let's call it that! The literal translation would be 'retmesagxo' or maybe 'retletero', but it's fine to simply say 'mesagxo' - we all know what we're talking about, after all.

"Skribado" is probably best used in this kind of context:

"Oni uzas skribilon por skribado" - You use a pen for writing (So, here 'writing' refers to the general action of writing)

I would also say that 'skribo' is a far too vague word to use in the context of thanking someone for a letter or email.

"Skribo" can have the same meaning as 'skribado' - the general idea of 'writing'...

"Skribo" could also possibly mean a 'skribajxo', which literally means 'something that is written' or 'a piece of writing'. Again, a very general term... ReVo gives this example:

"Sur la memorŝtono estas skribaĵo" - There's an inscription/something written on the headstone/gravestone.

"Dankon pro via skribajxo" sounds like "Thank you for your piece of writing". (A rather odd way of putting it!)

Ok, so maybe the use of 'skribajxo' is not a mistake - after all, it can in theory mean pretty much any type or 'writing', and we can understand what is meant in the context... But it's such a general term!

Here's another example of 'skribajxo' (taken from the 'tekstaro'):

"La plej malnovaj skribaĵoj slavlingvaj estis faritaj per literoj Latinaj kaj grekaj" - The oldest slavonic writings were done in Latin and Greek letters. - "Skribajxoj" is good here, as it refers to all sorts of things written!

Chainy:"Skribado" is probably best used in this kind of context:

"Oni uzas skribilon por skribado" - You use a pen for writing (So, here 'writing' refers to the general action of writing)

I would also say that 'skribo' is a far too vague word to use in the context of thanking someone for a letter or email.

"Skribo" can have the same meaning as 'skribado' - the general idea of 'writing'...

Of course, I just put "skribo/skribado" in there because I have no idea what context he's looking for