Zend error sending mail in 8.5.1 with PHP 7.0.33

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I am seeing this error upon form submission. Concrete5 v8.5.1 With PHP v 7.0.33. One form is using the Formify plugin and one uses the native form block. Both are configured to send email notifications. Both produce this error upon submit.
"Mail Exception Occurred. Unable to send mail: Zend\Mail\Header\ContentType::setType expects a value in the format "type/subtype"; received ""


Status: New
mmsd

concrete5 Environment Information

# concrete5 Version
Core Version - 8.5.1
Version Installed - 8.5.1
Database Version - 20190301133300

# concrete5 Packages
Afixia: SEO Redirects (1.1.2), ExchangeCore reCAPTCHA (1.1.1), Formify (3.2.3), HonestWebsites Store location (1.4.0.1), List files from set (1.0.13), Page Activity (0.9.3), Video Lightbox (2.3), Vivid Simple Accordion (1.0.1), Whale Responsive Tables (1.2.0)

# concrete5 Overrides
blocks/next_previous/templates/mg_next_prev/view.php, blocks/next_previous/templates/mg_next_prev, blocks/next_previous/templates, blocks/next_previous, blocks/page_list/templates/thumbnail_grid/view.php, blocks/page_list/templates/thumbnail_grid/view.css, blocks/page_list/templates/thumbnail_grid, blocks/page_list/templates/mg_blog/view.php, blocks/page_list/templates/mg_blog/view.css, blocks/page_list/templates/mg_blog, blocks/page_list/templates, blocks/page_list, blocks/image_slider/templates/mg_home/view.php, blocks/image_slider/templates/mg_home/view.css, blocks/image_slider/templates/mg_home, blocks/image_slider/templates, blocks/image_slider, blocks/video_lightbox/css/view.css, blocks/video_lightbox/css, blocks/video_lightbox, blocks/hw_store_location/view.php, blocks/hw_store_location, blocks/add_store/form.js, blocks/add_store/db.xml, blocks/add_store/view.php, blocks/add_store/add.php, blocks/add_store/controller.php, blocks/add_store/edit.php, blocks/add_store, blocks/autonav/templates/main_nav/view.php, blocks/autonav/templates/main_nav, blocks/autonav/templates, blocks/autonav, controllers/single_page/retailers/orderpop/products/detail.php, controllers/single_page/retailers/orderpop/products, controllers/single_page/retailers/orderpop/stores/manage.php, controllers/single_page/retailers/orderpop/stores, controllers/single_page/retailers/orderpop/cart.php, controllers/single_page/retailers/orderpop/orders.php, controllers/single_page/retailers/orderpop/orders/detail.php, controllers/single_page/retailers/orderpop/orders/edit.php, controllers/single_page/retailers/orderpop/orders, controllers/single_page/retailers/orderpop/stores.php, controllers/single_page/retailers/orderpop/purchase.php, controllers/single_page/retailers/orderpop/products.php, controllers/single_page/retailers/orderpop, controllers/single_page/retailers/orderpop.php, controllers/single_page/retailers, controllers/single_page/login.php, controllers/single_page/dashboard/poporder/products/form.php, controllers/single_page/dashboard/poporder/products, controllers/single_page/dashboard/poporder/stores/approvestore.php, controllers/single_page/dashboard/poporder/stores/edit.php, controllers/single_page/dashboard/poporder/stores, controllers/single_page/dashboard/poporder/orders.php, controllers/single_page/dashboard/poporder/orders/add_old.php, controllers/single_page/dashboard/poporder/orders/detail.php, controllers/single_page/dashboard/poporder/orders/add.php, controllers/single_page/dashboard/poporder/orders/edit.php, controllers/single_page/dashboard/poporder/orders, controllers/single_page/dashboard/poporder/stores.php, controllers/single_page/dashboard/poporder/products.php, controllers/single_page/dashboard/poporder, controllers/single_page/dashboard/reports/logs.php-, controllers/single_page/dashboard/reports, controllers/single_page/dashboard, controllers/single_page/register.php, controllers/single_page, authentication/concrete/form.php, authentication/concrete/email_validated.php, authentication/concrete/controller.php, authentication/concrete, jobs/send_to_fulfillment_api.php, jobs/geotag_stores_before_import.php, jobs/clear_empty_workflow_progress.php, single_pages/distributor/orderpop.php, single_pages/distributor, single_pages/retailers/orderpop/purchase/view.php, single_pages/retailers/orderpop/purchase, single_pages/retailers/orderpop/products/detail.php, single_pages/retailers/orderpop/products/view.php, single_pages/retailers/orderpop/products, single_pages/retailers/orderpop/stores/view.php, single_pages/retailers/orderpop/stores/manage.php, single_pages/retailers/orderpop/stores, single_pages/retailers/orderpop/orders/detail.php, single_pages/retailers/orderpop/orders/view.php, single_pages/retailers/orderpop/orders, single_pages/retailers/orderpop/view.php, single_pages/retailers/orderpop/cart/view.php, single_pages/retailers/orderpop/cart, single_pages/retailers/orderpop, single_pages/retailers, single_pages/login.php, single_pages/dashboard/hw_store_locations/approvestore.php, single_pages/dashboard/hw_store_locations/addstore.php, single_pages/dashboard/hw_store_locations, single_pages/dashboard/hw_store_locations.php, single_pages/dashboard/poporder/products/form.php, single_pages/dashboard/poporder/products/view.php, single_pages/dashboard/poporder/products, single_pages/dashboard/poporder/stores/approvestore.php, single_pages/dashboard/poporder/stores/view.php, single_pages/dashboard/poporder/stores/view.css, single_pages/dashboard/poporder/stores/edit.php, single_pages/dashboard/poporder/stores, single_pages/dashboard/poporder/orders/detail.php, single_pages/dashboard/poporder/orders/add_old_tmp.php, single_pages/dashboard/poporder/orders/view.php, single_pages/dashboard/poporder/orders/add.php, single_pages/dashboard/poporder/orders/edit.php, single_pages/dashboard/poporder/orders, single_pages/dashboard/poporder, single_pages/dashboard/reports/linkchecker.php, single_pages/dashboard/reports/logs.php, single_pages/dashboard/reports, single_pages/dashboard, single_pages/register.php, themes/milorganite/page_forbidden.php, themes/milorganite/page_not_found.php, themes/milorganite/blog_landing.php, themes/milorganite/landing_retail.php, themes/milorganite/testimonial_viewer.php, themes/milorganite/videos.php, themes/milorganite/landing.php, themes/milorganite/blog_post.php, themes/milorganite/js/bootstrap.min.js, themes/milorganite/js/jquery.matchHeight-min.js, themes/milorganite/js/flaunt.js, themes/milorganite/js, themes/milorganite/main_content.php, themes/milorganite/content_text_retail.php, themes/milorganite/content_text_pro.php, themes/milorganite/elements/header_retailer.php, themes/milorganite/elements/header_top.php, themes/milorganite/elements/footer_bottom.php, themes/milorganite/elements/header.php, themes/milorganite/elements/orderpop_header.php, themes/milorganite/elements/footer.php, themes/milorganite/elements/header_pro.php, themes/milorganite/elements, themes/milorganite/blank.php, themes/milorganite/description.txt, themes/milorganite/left_sidebar.php, themes/milorganite/home_pro.php, themes/milorganite/thumbnail.png, themes/milorganite/home.php, themes/milorganite/main_content_pro.php, themes/milorganite/home_retailer.php, themes/milorganite/landing_pro.php, themes/milorganite/view.php, themes/milorganite/default.php, themes/milorganite/search_results.php, themes/milorganite/page_theme.php, themes/milorganite/contact.php, themes/milorganite/content_text.php, themes/milorganite/main_content_retail.php, themes/milorganite/blog.php, themes/milorganite/images/cork-lt.png, themes/milorganite/images/hamburger.svg, themes/milorganite/images/MilorganiteLogo.png, themes/milorganite/images/cork-bkg.png, themes/milorganite/images/arrow.svg, themes/milorganite/images, themes/milorganite/css/overrides.css, themes/milorganite/css/default.css, themes/milorganite/css/bootstrap-modified.css, themes/milorganite/css/modal.css, themes/milorganite/css/flaunt.css, themes/milorganite/css, themes/milorganite/faq.php, themes/milorganite/full.php, themes/milorganite

# concrete5 Cache Settings
Block Cache - On
Overrides Cache - On
Full Page Caching - On - If blocks on the particular page allow it.
Full Page Cache Lifetime - Every 4600 minutes.

# Server Software
Apache

# Server API
cgi-fcgi

# PHP Version
7.0.33

# PHP Extensions
bcmath, calendar, cgi-fcgi, Core, ctype, curl, date, dom, fileinfo, filter, ftp, gd, hash, imap, json, libxml, mbstring, mcrypt, mysqli, mysqlnd, openssl, pcntl, pcre, PDO, pdo_mysql, pdo_sqlite, Phar, posix, readline, Reflection, session, SimpleXML, sockets, SPL, sqlite3, standard, tokenizer, wddx, xml, xmlreader, xmlwriter, xsl, Zend OPcache, zip, zlib

# PHP Settings
max_execution_time - 300
log_errors_max_len - 1024
max_file_uploads - 20
max_input_nesting_level - 64
max_input_time - 600
max_input_vars - 1000
memory_limit - 2048M
post_max_size - 150M
sql.safe_mode - Off
upload_max_filesize - 100M
mysqli.max_links - Unlimited
mysqli.max_persistent - Unlimited
pcre.backtrack_limit - 1000000
pcre.recursion_limit - 100000
session.cache_limiter - <i>no value</i>
session.gc_maxlifetime - 7200
opcache.max_accelerated_files - 4000
opcache.max_file_size - 0
opcache.max_wasted_percentage - 5

Browser User-Agent String

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.131 Safari/537.36