Mailscale

Mailscale gradually sends low-volume, natural-looking emails from new accounts to build sender reputation over time. The platform owns full infrastructure including SMTP servers and IP pools. With 95-100% deliverability claims for Gmail and Outlook, users can expect 40-70% open rates, which is 2-3 times higher than the average international email open rate of 21%. However, there is a setup waiting period of a few weeks before campaigns can begin.