jcolliez

Allingroups lets you automatically publish a message, as if you were writing each one individually, to all of the Facebook groups that you select.
In a few clicks, you can start a campaign that you can follow in real time on your <a href="http://connect.allingroups.com/" title="Allingroups dashboard" rel="nofollow ugc">dashboard</a>.
You can also save your group playlists so that you can use them again in new campaigns. Additionally, you can join groups matching your search criteria automatically.
IMPORTANT: This plugin requires a valid Facebook account, the plugin will ask it and use it to create an account remotely on http://connect.allingroups.com/ , so the plugin will send your informations through the network in https requests to allingroups API.

Allingroups

Allingroups lets you automatically publish a message, as if you were writing each one individually, to all of the Facebook groups that you select.

sendmachine

Sendmachine’s official plugin will enable you to:
Set up signup forms 
You can set up a signup form in a few easy steps: connect using the provided API <a href="https://www.sendmachine.com/admin/#/myaccount/smtp_settings" rel="nofollow ugc">credentials</a>, select a contact list where your visitors will subscribe and you’re basically good to go. The signup form is available as a widget (in your widget area) or as a shortlink by pasting <code>[sm_subscribe_form]</code> in a post or page.
Add subscribe checkboxes 
Allow users to subscribe to your contact list only by checking a checkbox in certain website areas like comment form or register form.
Sync your wordpress users with a specific contact list 
You want to send emails to all your users but don’t know how? Well, don’t worry, we can help you with that. After you’ve successfully selected a contact list, you can use the “Sync users” button, to subscribe all your users to that contact list.
Send emails through our services 
No need for nasty, geeky configurations. Just set a from email, an optional from name and you are good to go. Also, make sure that “enable email sending” is set to <code>on</code>. 
If you set a from email that doesn’t already exist in your sendmachine account as a sender address, a confirmation email will be generated and sent to that address. 
Not quite sure if you’ve done everything right? You can test if everything is ok by sending a test email. If you got the mail, you can sit back and relax: you’ve done it, otherwise something went wrong.
Send transactional emails 
No more “dog ate my email” excuses. Using our services you can now monitor an email’s activity (opens, clicks, geolocations, user agents). In order to enable this option, after you install our plugin, go to “email settings” tab and check that “Register” and/or “Comment” checkboxes. Basically, if you tick that checkboxes on each email sent, that coresponds with that action, we add a custom tracking header: <code>X-Sendmachine-Campaign: campaign_name</code>, where campaign_name is the name of the transactional campaign that will be created, or updated if already exists. Campaign’s name can be found/modified next to every action’s checkbox.
Send news feed 
You can send a newsletter directly from the admin panel with the latest posts. You can choose to build your newsletter with the latest 5, 10, 15 or 20 posts, set newsletter’s width, color and content.

Sendmachine for WordPress

Official Sendmachine plugin featuring subscribe forms, users sync, news feed, email sending and transactional campaigns.

Allingroups vs Sendmachine for WordPress