How to Unblock a Sender?

To unblock a sender previously blocked using BlueMail's Spam feature, either:

Open the blocked email in the Spam folder, tap the 3-dot menu, and select Unblock Sender. See How Do I Manage Spam?
Remove the address or domain from your Block List directly. See How Do I View/Edit the Block List?

Spam folder → 3-dot menu → Unblock Sender

Still Going to Spam After Unblocking?

Unblocking only clears your Block List, and that is not the only thing that can move a message to Spam:

BlueMail's Block List: the addresses and domains you blocked yourself. Cleared by Unblock Sender, or by removing the entry under Settings | Accounts | [select the account] | Blocked Senders. See How Do I View/Edit the Block List?
Your email provider's spam filter: runs on the provider's servers, before BlueMail sees the message. BlueMail cannot override it. If the provider caught the mail, fix it in your provider's own webmail; nothing you change in BlueMail will release it.

If unblocking a sender made no difference, the provider is the one filtering the message, and it has to be fixed on the provider's side.

How Do I Make Sure a Sender Always Reaches Me?

On BlueMail's side, unblocking is all it takes and it applies immediately, your Block List holds only what you put on it, so removing an entry restores normal delivery. That single list is deliberate: one screen shows every blocking decision you have made, with nothing tucked away in a second, competing list to contradict it.

For a standing "always deliver this sender" rule, use your provider's allowlist or filter rules, Gmail's Never send it to Spam filter, for example. Those run on the server before any mail app receives the message, so one rule covers BlueMail and every other place you read your mail.

What you can do instead:

Unblock the sender, or remove the address or domain from your Block List.
If BlueMail's own filtering is catching too much, set Spam Filter to Low or Off at Settings | Privacy & Security | Advanced Features. See Blue Guard
If your provider is catching it, use whatever "not spam" or safe-sender control your provider offers in its webmail. That one is out of BlueMail's hands.