Hi,Hi @madde1000, I believe you are referring to the Mumara Classic edition. Yes for the reason we have removed it from our further editions for the fact that clients are misunderstanding the purpose. When Mumara verified the validity of an email address, it sends certain SMTP commands to the recipient server and gets a response. It's very usual that the recipient server finds spam behavior from your Mumara server's main IP address and blocks it. Once the IP gets blocked, Mumara's hands get tight and it keeps spinning the wheel instead of getting any signal. So clients usually think that email verification just depends on Mumara's coding but it's actually your server IP that is sending SMTP commands and Mumara's being just an agent to send packets and receive a response. I highly suggest using a third-party service to validate your lists.