I personally think from my Email Marketing experience of last couple of years that Postfix is better than PowerMTA to deal with as an MTA.
>> Postfix:
Open Source
Free
Best for StartUps & SME’s.
Usually best for all requirements.
Quick.
Customized scripts/wrappers needed for Dashboard.
>> PowerMTA:.
Closed Source.
Really Costly.
Best for Enterprises.
Customized for ESP’s.
Really Fast.
PMTA Management Console offered.
Hotmail, Gmail, Yahoo, QQ, RoadRunner, AOL, Orange.fr or any XYZ Email Providers in the entire world has a clear cut guideline specified for accepting e-mails in their network.
Which is to provide a track record & score to an inbound e-mail sending out server’s IP Address & Domain & therefore enabling ONLY those lots of e-mails in a window duration based on it’s track record respectively.
Duration.
Now, even if we have a tool or rather specifically an outgoing e-mail sending out engine to send out e-mails as quick as possible, then too we are absolutely depending on the getting server’s guideline to accept e-mails from our end.
Our e-mails to get accepted & not get bounced, we have to Rate-Limit the outgoing e-mail servers.
It suggests to own a quick & effective e-mail sending out engine does NOT make good sense, as in case it’ll be rate-limiting the outgoing IP’s to be in usage, whether we have our MTA as Postfix or PowerMTA.
What matters absolutely is NOT to SPAM & have an Opt-In List.
Much better to have a Double Opt-In List, if possible.
All the Big & Major ISP’s like Yahoo, Gmail & Hotmail, and so on are extremely clear about accepting e-mails from which servers. Whom to accept & whom to turn down & whom to enable partly. They keep altering their algorithms as it matters a lot to keep the Spammers away.
IP Reputation & Domain Reputation is the KEY to Success in the Email world.:-RRB-.
As around 2+ Billion e-mails are sent out daily & less than 5% are genuine e-mails. Rest is SPAM.
Focus ought to be on Deliverability instead of the e-mail sending out Speed.
[Speed is the speed of outgoing e-mails that are sent out from a server or rather an IP to be accurate.
Deliverability is the capability to Deliver e-mails in the INBOX of the e-mail recipient & Not in the Spam folder.]
And to accomplish optimum Deliverability, there are N variety of methods & strategies to be executed in due course of time. It is a never ever ending video game & get’s more tough & fascinating as the outgoing e-mail volume boosts.