Add workflow automation builder for campaigns (onboarding, drip sequences, conditional logic)

It would be highly valuable to introduce a **visual workflow automation builder** for email campaigns, enabling users to create advanced sequences without writing code.

Feat: Ability to manage click / open tracking per campaign

Currently its linked to domain.

Allow setting a custom domain for click & open tracking

Currently, UseSend uses the default AWS SES tracking links for click and open tracking. Since these tracking domains are shared across many users, all links look the same from a deliverability perspective.

SES Callback status: Failed

in Self Hosted version:

feat(feedback): save feedback in the database, with an admin API to list, reply and import

Feedback from the dashboard's Feedback button is now saved in the database before anything is emailed, so it isn't lost when the email fails, and it can be listed and answered from our own tools. Same design as split-pro-cloud #50, adapted to useSend.

🐞 - Saved campaigns can't be edited on v1.10.x

### What happened?

🐞 - Whitespace inside {{var, fallback=...}} ends up in the rendered text

### What happened? Whitespace inside a contact variable with a fallback ends up in the rendered text. With an empty `firstName`, the subject `Hi {{ firstName, fallback= there }}, welcome!` renders as `Hi there , welcome!`, with an extra space on each side of the fallback. `{{firstName,fallback=there}}` without padding

Account for every SES recipient in email send-rate limiting

## Summary

Honour the SES send rate per second and retry throttled sends

## Summary

fix: render text-only emails in the email preview

## Problem

SMTP proxy sends raw RFC 5322 recipients, which the public API schema rejects (invalid_string on "to")

Every message relayed through `usesend/smtp-proxy` whose `To` header carries a display name is rejected by useSend own public API, so it never leaves the proxy.

fix: allow self-hosted GitHub users without email

## Summary

fix: restrict self-hosted registration

## Summary

fix: sandbox campaign preview in iframe to prevent style leakage

Closes #409

🐞 - Emails stay stuck in "Queued" forever when a sending limit is exceeded

### What happened?

🐞 - Callback Success, but all emails appear as 'Queued'

### What happened?

Add warm-up / throttled sending for large email campaigns

When sending emails to a large subscriber list (e.g., 50,000+ recipients), it would be extremely helpful to have a built-in **warm-up / throttling feature** to improve deliverability and reduce the risk of being flagged as spam.

Feature Request: Customizable DNS Records (DKIM Selector, MAIL FROM, Tracking Domains)

## Problem Currently, when adding a domain in Usesend, DNS records are automatically generated with fixed naming conventions: - DKIM selector: `usesend._domainkey` - MAIL FROM: `mail.<domain>`

🐞 Database connection does not retry after server restart

### What happened?

Add Support for Email Receiving

Currently, the system supports sending emails but does not handle incoming messages. Please add functionality for receiving emails, including parsing, storing, and making them accessible through the UI or API.

Feat: 2-Step verification for adding contacts via API (GDPR)

To comply with GDPR, some customers needs a 2-step verification before adding to a contact list.