Mail send problem (hangfire)

Hello everyone, my friend and I are working on a bulk email sending system. We got hosting, but when we logged out of the site, it would stop sending emails. So we switched to a Windows server. However, now we are facing another issue: the emails are not being sent. On the Hangfire dashboard, everything shows as “success,” but no emails are actually being delivered. We’re using an external SMTP service, not our own. What could be causing this issue?