What is the reputation of an IP or Domain?

By defining it in a quick and simple way, it is one of the main filters used by any email provider to decide what to do with the emails sent from your IP and Domain, whether to let them go to the inbox, whether to send them to spam, or whether to directly block them from entering.

Why do the emails I send not arrive at their destination or they arrive to the Spam folder?

There are many factors behind this, from blacklisting, spam lists of both the IP and the domain itself, poor configuration of the mail server and a long etc.

How long does it take to clean an IP that is on SPAM lists?

It depends a lot on how many SPAM lists you are on and what lists you are on, because it is something we manage but it does not depend directly on us but on the companies that manage these lists, normally within 30 days your IP should be out of all spam lists, but it is not something exact is an estimate.