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Fastmail does not have a feature they call "multiple inboxes". But you can create multiple folders or labels (they look the same with a user interface similar to file folders), and cause certain emails to appear in the proper "inbox" when they are delivered to your account. And, of course, you can drag (or move with a tool) messages between the "inboxes" (folders or labels). Each folder/label/"inbox" can be named as you wish. For compatibility reasons, there can be only one folder/label named "Inbox" to allow email client software to find that location to retrieve messages if you don't automatically file messages upon receipt. But you can create "Auto Inbox" for Automobile related messages about your vehicles, "Medical Inbox" for medical related messages, and subfolders such as "Medical Inbox > Insurance".
You can reorder each folder/label/"inbox" as you wish in the listing. So you could create an "Auto Inbox" at the top, "Medical Inbox" next, and place "Inbox" next to receive all other incoming messages, for example.
Fastmail recently (in late 2023) added a new user interface feature to make it easier to get messages sent to a particular alias (email address) to be automatically be filed into a folder/label/"inbox". See:
There are multiple methods you might want to use to get incoming messages delivered to the correct folder/label/"inbox":
- Special email addresses: Fastmail allows you to create up to 600 aliases (email addresses) at Fastmail-owned domains. If you own a your own domain, you can use custom domains with Fastmail. This allows you to separate different categories using specialized email addresses. So you could sign up for several newsletters using "newsletter@example.org" and medical related services using "medical@example.org", where "example.org" is either a Fastmail domain with that available alias or a domain you personally own or control.
- Rules (automatic filing) based on the sender From address.
- Rules (automatic filing) based on the subject line of the message.
- Rules (automatic filing) based on some character string in the message body.
- Rules (automatic filing) based on some message header.
- Rules (automatic filing) based on a mailing list ID.
- You can add a rule from a particular email easily by choosing in the Actions... tool to Create rule from message ...
If you use folder mode, each message appears to be located in one particular folder. Label mode allows multiple labels to be applied to a particular message. You can switch back and forth between folder and label mode -- if you add multiple labels to a message, it will appear in multiple folders if you switch to folder mode.
Fastmail has a free iOS/iPadOS and a free Android app, as well as access using a web browser or an email client (such as Outlook, Thunderbird/Supernova, or Apple Mail). Every day I use my iPhone, iPad, and Windows web browser with Fastmail at different times of the day. I have the Fastmail calendar synchronized with my iPhone calendar.
I hope I haven't overloaded you. Please ask any specific questions you have about how Fastmail works and I (or someone else) will be glad to help.
Bill