You like it or not, not all the email addresses that you will be using will be valid, there are many reasons why a valid email address can become invalid, we will not cover that, instead, we will cover the tool that will make sure once an email address becomes invalid, you will know.

Almost any email account can be used as a bounce server Again, this is correct and true if you have IMAP and/or POP3 access to your email provider. Please ask your provider in case you are not sure.

The bounce servers are used to process the emails that will not reach their destination, that is, the email address does not exist anymore, or it is not available, etc.
When this happens, the email will be returned back to your bounce server and the bounce server will process it and decide what action should take against the problematic email address.
There are two main types of bounces, HARD and SOFT.

HARD bounces When an email is returned and gets labeled as a HARD bounce, usually this means you should stop the delivery for that address and blacklist it.
MailWizz EMA will do this automatically for you, depending on your backend settings.
If a email address is blacklisted but you know it is valid again, you can just remove it from blacklist.

SOFT bounces When an email is returned and gets labeled as a SOFT bounce, usually this means you should not stop the delivery for that address.
A SOFT bounce might be an autoresponder the subscriber has put in place while he is in vacantion, or might be a temporary error on the recipient server if that server runs out of storage space for that particular subscriber.
However, there are cases when a email address will always return SOFT bounces, in this case you waste your resources trying to deliver the email for that address.
In order to prevent this exact behavior, MailWizz EMA allows you to configure the SOFT bounce limits and remove unwanted addresses.

Bounce servers are optional Yes, this is true.
You are not forced to add and use a bounce server, but if you don't, then the entire bouncing mechansim will not work, that is, you will not get statistics about campaign bounces and you will never know which email address is good and which not.
Please note that you can use a GMAIL account or any other provider as your bouncing account.