doublesharp

<h4>Validated Field Add-On</h4>
The Validated Field add-on for <a href="https://wordpress.org/extend/plugins/advanced-custom-fields/" rel="ugc">Advanced Custom Fields</a> 
provides a wrapper for other input types which allows you to provide client side input masking using the jQuery 
<a href="http://digitalbush.com/projects/masked-input-plugin/" rel="nofollow ugc">Masked Input Plugin</a>, server side validation using either PHP regular expressions 
or PHP code, the option of ensuring a field’s uniqueness for all posts by <code>post_type</code> and <code>meta_key</code>, <code>post_type</code>, or site wide, or a 
single post by meta_key, as well as marking a field as read-only. Edit your fields in the ACF Field Group editor and update code using the ACE.js 
IDE with autocomplete and syntax validation.
<h4>Features</h4>
<ol>
<li>Input Masking – easily set masks on text inputs to ensure data is properly formatted.</li>
<li>Server-Side Validation – validate the inputs using server side PHP code or regular expressions.</li>
<li>Uniqueness – ensure that the value being updated is not already in use.</li>
<li>Repeater Fields – validated fields within a <a href="http://www.advancedcustomfields.com/add-ons/repeater-field/" rel="nofollow ugc">Repeater Field</a>.</li>
<li>Read Only – specify a field as read-only allowing it to be displayed but not updated.</li>
<li>WordPress Multi Language – compatible with multilingual sites using the WPML plugin.</li>
<li>Conditional Logic – show and hide validated fields based on the values of other “switch” fields.</li>
</ol>
<h4>Compatibility</h4>
Requires <a href="https://wordpress.org/extend/plugins/advanced-custom-fields/" rel="ugc">Advanced Custom Fields</a> version 4.0 or greater.

Advanced Custom Fields: Validated Field

Adding my one star to inform people that this plugin is no longer working

Doesn't work in ACF Pro 5.6.2

The Validated Field add-on for Advanced Custom Fields provides input masking and server-side validation of other field types.

adaptsites

Kegan Quimby

This plugin adds filters to the WordPress user registration process. It lets you check user signups against StopForumSpam.com and/or Emailable.com
When a user registers, you can configure this plugin to use the submitted email address and IP address to first check against StopForumSpam.com to see if there is a match to the IP address and/or the email address in their FREE database. Then you can check if the ending of the email address is .ru or another country extension you want to block to cut down on spam registrations. Finally, if it passes these checks, you can check the email address against Emailable.com to see if the email is valid.
<a href="https://emailable.com" rel="nofollow ugc">Emailable.com</a> 
Validate user registration emails using Emailable.com to see if an email is: deliverable, risky, unknown, or undeliverable.

Add Spam Filters

Stop Spam User Registrations by Adding StopForumSpam.com, Emailable.com, and Email Domain Extension Filters.

Advanced Custom Fields: Validated Field vs Add Spam Filters