Depends on what you're doing.
If it's just for your own outbound, Mailforge, Maildoso, and Mailscale can all work if your volume is reasonable and you know how to manage domains, warmup, bounce rate, copy, tracking, and so on. Wouldn't pick purely based on "cheapest inbox" - cheap inboxes are useless if the setup gets fried in two weeks.
For getting clients, what you should care about is the system around the inboxes:
- separate domains per client
- separate mailboxes and users
- proper SPF, DKIM, and DMARC
- a slow ramp-up
- bounce and reply monitoring
- no shared messy reporting
- ability to see each client's performance independently
- not using the client's main brand domain
Mailforge and Maildoso are decent if you want fast inbox and domain setup. Mailscale makes sense if you're managing a larger pool of inboxes. But for client outreach, you'd want more control than just "here are 50 inboxes."
That's where something like SMTPProvider comes in: setting up the sending infrastructure, domain and authentication setup, IP routing or rotation where needed, bounce and log monitoring, and separate client- and team-level setup so you're not mixing data across clients. It's more useful when you're running outreach as a service and need cleaner control and reporting, not just random inbox creation.
Also, no provider can honestly guarantee inboxing. The provider matters, but list quality, copy, domain age, sending pattern, bounces, and replies matter just as much.
