form submission occasionally doesn't trigger email

I have two forms configured with “from” email address that comes from the form itself.

I have seen emails missing from both these forms, and the interesting part to me is the missing emails are “from” yahoo.com addresses. I have not seen missing transmissions from other addresses, except when I mistyped “yahoo.com” as “hahoo.com”.

I suspect something is checking if this is a valid “from” address, which is failing the check.

Not sure if this is ninja forms problem, php problem or something yahoo.com is doing wrong.

I need to figure out a workaround, in any case.

My forms are at http://steeplechasers.org/about/suggestion-box/ and http://steeplechasers.org/competition/racing-team/racing-team-application/ if that helps.

### Environment ###

Home URL: http://steeplechasers.org
Site URL: http://steeplechasers.org
Ninja Forms Version: 2.8.13
WP Version: 4.1.1
WP Multisite Enabled: No
Web Server Info: Apache
PHP Version: 5.3.24
MySQL Version: 5.5.40
PHP Locale: decimal_point: .thousands_sep: int_curr_symbol: currency_symbol: mon_decimal_point: mon_thousands_sep: positive_sign: negative_sign:
WP Memory Limit: 40 MB
WP Debug Mode: No
WP Language: Default
WP Max Upload Size: 32 MB
PHP Post Max Size: 33 MB
Max Input Nesting Level: 64
PHP Time Limit: 30
PHP Max Input Vars: 1000
SUHOSIN Installed: No
SMTP: relay-hosting.secureserver.net
smtp_port: 25
Default Timezone: Default timezone is UTC

### Plugins ###

Installed Plugins: Advanced Excerpt by Delicious Brains version 4.2.3
Breadcrumb NavXT Remove Current Item Extension by John Havlik version 1.0.1
Breadcrumb NavXT by John Havlik version 5.2.0
CPK Ultimate Archives by CPK Web Solutions version 1.0
Custom Facebook Feed by Smash Balloon version 2.3
Div Shortcode by Bill Erickson version 2.1
Duplicator by LifeInTheGrid version 0.5.12
Event Rocket by Barry Hughes version 2.5
HTML Widget Text by Jaimyn Mayer version 1.00
HTML5shiv by Ramoonus version 3.7.2
MaxButtons by Max Foundry version 1.34
MCE Table Buttons by Jake Goldman
10up
Oomph version 3.2
Ninja Forms by The WP Ninjas version 2.8.13
Page-list by webvitaly version 5.0
PHP Browser Detection by Mindshare Studios
Inc. version 3.1.2
Go Daddy Quick Setup by GoDaddy.com
LLC version 1.04
Rewrite Rules Inspector by Daniel Bachhuber
Automattic version 1.2.1
Simple Full Screen Background Image by Pippin Williamson version 1.1
Slideshow Gallery by Tribulant Software version 1.5.3
Table of Contents Plus by Michael Tran version 1408
The Events Calendar by Modern Tribe
Inc. version 3.9.1
Welcome to WordPress by Starfield Technologies version 1.0
WP Edit by Josh Lobe version 3.0.1
WP Security Audit Log by WP White Security version 1.3.3

https://wordpress.org/plugins/ninja-forms/