What do the risk ratings mean?
We rate 40 different validity criteria for each email ID. In some cases these criteria are consolidated at the domain level, in some cases it applies to the mailbox. At the end of the day, we give an internal score out of 40 for each email.
Domain Unsafe: The domain was found to be unsafe - either it didn't have an MX record, or is heavily blacklisted for being a spam-source or is a recognized spam-trap domain. This rating can also be hit if its a known dangerous domain (i.e. reply emails are forwarded to spam lists), or disposible domains (i.e. email ids can be discarded in seconds and are not reliable).
Email Unsafe: The email ID itself was found to be either invalid (550) or always gives a mailbox full type message. Email IDs that are flagged as regular complainers (i.e. stats from our historic campaigns go here), email ids on public domains that are set to foward to spam-traps (yes!) or other generally bad quality email ids (eg. firstname.lastname@example.org or email@example.com - which seem valid but aren't).
Medium Risk: A combination of domain risk factors and email risk factors, but with a combined score of around 10 on 40. There are some unforgivable criteria (in which case even 1/40 can result in an 'unsafe' marking)
Low Risk: Use these. No problem. Don't spam them though; they are probably humans which means if they complain you are at risk! :)
Why does it take so long?
Mailmule isn't a magic wand. That apart, we actually validate the email IDs you submit - and doing 40 validations
per email ID certainly takes time! In fact it takes around 18 seconds per email ID (which would mathematically come to 50 hours for a list of 10,000 emails, right?)
We are able to complete validations pretty fast given we have a total of 40 servers across which we balance the load.
But in some cases, it takes extremely long - specially when there's a lot of greylisted ids involved. It's impossible to validate a greylisted email id until the greying is lifted; and for some servers that's 1-2 minutes (It was 18 seconds for 1 id, remember? This now makes it around 40-45 seconds per email id on average.)
That's why we ask for 24-48 hours. It's not that we want to give you the results late; far from it - we want you to have the highest quality result possible!