If you have high volumes, give a try to our MailUp since it can be particularly affordable in certain cases.
MailUp has an unique pricing model called “pay-per-speed”. This allows you to save a lot if you accept a delayed sending.
Let … (more)

It's not open source, but it has a free edition with unlimited users: https://beefree.io/email-editor-embeddable-component/

If you are above 2,000 recipients, have a look to our MailUp.
We have an unique pricing model called “pay-per-speed”. This allows you to save a lot if you accept a delayed sending.
Let me explain. If you need to send 50,000 … (more)

If you still need to use Outlook, you may be interested in the SMTP+ option in MailUp. You can:
a) send adding thousands of subscribers in BCC. MailUp will send the message to each recipient in the TO: fields (BCC to … (more)

I suggest: BEEfree.io (free, with editor) Themeforest (paid) EmailMonks (agency)      

BEEfree.io offers free responsive templates with a great free editing tool.

I suggest this website: www.emailvendorselection.com. It lists almost all the main ESP around the world.
On my side I can add the our MailUp has an unique pricing model called “pay-per-speed”. This allows you to save a lot if you accept … (more)