When email address are validated there are a number of steps that must be executed, each of which takes time to get right.

In general, the “Validating” phase of the process takes around 5 minutes + 1 minute for each 1,000 addresses. So, a validation of 3000 email addresses will take approximately 8 minutes.

If the process encounters a server with “greylisting” then an additional 15 to 20 minutes will be needed to undertake the “Anti-Greylisting” process.