I need to send about ~20k emails to potential clients and need the best way to avoid:
I've searched a few forums and people said it's best to send mails in 1k packages but my question is what delay between sending each 1k should I set? I mean 1k/day or 1k/hour or 1k/min etc.
I recently had to build system to do so, here is the solution we chose :
1- The management system setup emails and store them in a database.
2- We setup a no-reply account on our mail server to get the bounces back.
3- We build a small code over the great mailing library swiftmailer (swiftmailer.org).
4- We run the script we build through a cron and send mails in packages of 50 per minute (hotmail will most likely flag email as spam if too much emails are sent from the same adresse/server in the same minute). We store each swiftId i the mail database
5- At the runtime of the mail sending script we check for bounces or other errors in our no-reply mailbox and flag our messages in our mail table accordingly (status : 1 - success, 2 - invalid email, 3 - bounces)
6- We sync back our data (upon user accessing the section of the system) in the main system when they have a status and that the last change was made at least 10 minutes in the past to limit the change of states in the system. (the synchronisation script can change the status of an item in the main system, but the 10 minutes delay reduce the risk of changes)