You unique filter ID looks something like this #8WY and can be found in the signature of every email that mailivery sends to your account.

Since the implementation of our automatic "email reading" feature, most users wont need to use their filter ID anymore, however it does still serve two crucial purposes, custom email filters and conditional forwarding. The ID can also be useful to confirm which emails are from mailivery in case you accidentally move them to the wrong folder. If you receive a response to a mailivery email which does not contain your filter ID in the signature please let us know immediately.

Custom email filters ensure mailivery emails are moved out of your inbox and tagged accordingly in order to avoid confusing you, if for any reason you want to turn automatic email reading off, or it doesn't work as intended with your email server configuration.

Read the full article on how to set up custom email filter.

Conditional forwarding is important if you are forwarding incoming emails to an email account that is linked to mailivery, for two reasons.

Firstly, for instance forwarding mailivery interactions from an email you use for outreach to your primary email makes little sense and will be confusing - you only want to see emails from real people, and not interactions with mailivery from your forwarding address.

Secondly, setting up an unconditional forward from an email that is linked to mailivery can cause mailivery emails to bounce, which creates problems that ultimately harm your email reputation. 

Luckily, it is easy to set up a conditional forward in most email clients, so that mailivery interaction will not be forwarded to your main email account, but all other emails will.

Read the full article on how to set up conditional forwards.