How to set up a custom SMTP relay for Gmail, Outlook, or any IMAP account

This task can be performed using Cleanbox

Email aliases, AI spam filtering, and a full SMTP relay

Best product for this task

Cleanbox

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Cleanbox sits between the internet and your inbox. Every incoming email goes through spam scoring, virus scanning, AI classification, and your own rules before delivery. Create unlimited aliases that forward to your real inbox, build custom filters, and use Cleanbox as a complete SMTP relay. Works with Gmail, Outlook, iCloud, Yahoo, or any IMAP provider, no migration needed. Privacy-first: no advertising, no data selling, no user profiling.

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What to expect from an ideal product

1. Cleanbox works as a full SMTP relay, so you can send emails through Gmail, Outlook, or any IMAP account without touching your existing setup
2. You don't need to migrate anything — just point your outgoing mail through Cleanbox and keep using whatever inbox you already have
3. It lets you create unlimited email aliases that route back to your real address, which makes managing multiple sending identities much cleaner
4. Every email going in or out passes through spam filtering and AI classification, so your relay stays clean and your deliverability doesn't suffer
5. There's no advertising or data selling involved, which matters when you're routing business or personal email through a third-party service

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