That is not application giving an error, but your contacts server sending you a message with information that your contact inbox is full and this message will not be stored, so it will not receive it.

I think that the only thing you could do is to contact (in some other way) your contact and inform them that the inbox is full or just wait until your contact became online and cleans up the inbox.

The app was downloaded just yesterday. Is it somehow related to mail or messages on the phone?

The issue is with your contact account on their server, not with the app. It is not related to email or messages on the phone.

how can this problem be solved?

more encryption problems: I sent you an OMEMO encrypted message but your client doesn't seem to support that

@Olik2 can you join the support channel so you can get faster responses?

xmpp:tigase@muc.tigase.org?join