Form responses don't get mailed

Yesterday I've updated Perch to the latest version. Now the form responses don't receive my inbox. They are stored in Perch as usual, so the form itself is still working. I've tried to send a test-email, but that doesn't get mailed either. I was on Perch 2.8.33 and upgrade tot 2.8.34. Below is my diagnostics report. Does anyone know what's the problem?

Perch: 2.8.34
Production mode: Production (100)
Installed apps: content (2.8.34), assets (2.8.34), categories (2.8.34), perch_blog (5.0), perch_forms (1.8.3)
DB driver: PDO
DB tables: perch2_blog_authors (2), perch2_blog_comments (0), perch2_blog_index (274), perch2_blog_posts (5), perch2_blog_posts_to_tags (0), perch2_blog_sections (1), perch2_blog_tags (0), perch2_blogs (1), perch2_categories (0), perch2_category_counts (0), perch2_category_sets (1), perch2_content_index (152), perch2_content_items (87), perch2_content_regions (16), perch2_forms (1), perch2_forms_responses (1), perch2_navigation (0), perch2_navigation_pages (0), perch2_page_templates (1), perch2_pages (17), perch2_resource_log (620), perch2_resource_tags (0), perch2_resources (157), perch2_resources_to_tags (0), perch2_settings (23), perch2_user_passwords (0), perch2_user_privileges (38), perch2_user_role_privileges (24), perch2_user_roles (2), perch2_users (2)
Users: 2
PHPMailer: 5.2.21
App runtimes:
<?php
    $apps_list = array(
        'content', 
        'categories',
        'perch_blog',
        'perch_forms',
    );
Scheduled tasks for perch_blog: delete_spam_comments (1440 mins)
Editor plug-ins: markitup, redactor
H1: 1c185df2b3f61af28b2e7d787b4ff1af
L1: 19d867f683094ae6ec374b96b425d94f
F1: 6a33f95eca3667f9e0c39bf5ca2980fe
headerColour: #ffffff
content_singlePageEdit: 1
helpURL:
siteURL: /
hideBranding: 0
content_collapseList: 1
lang: en-gb
update_2.8.33: done
latest_version: 2.8.15
on_sale_version: 2.8.34
perch_blog_update: 5.0.1
perch_blog_post_url: /nieuws/{postSlug}
headerScheme: light
perch_blog_site_name:
perch_blog_slug_format: {postTitle}
perch_blog_akismet_key:
perch_blog_max_spam_days: 0
dashboard: 0
hide_pwd_reset: 0
content_hideNonEditableRegions: 0
content_frontend_edit: 0
perch_blog_comment_notify: 0
update_2.8.34: done
PERCH_DEVELOPMENT: 10
PERCH_STAGING: 50
PERCH_PRODUCTION: 100
PERCH_DB_USERNAME: flexiuy104_wpi
PERCH_DB_SERVER: localhost
PERCH_DB_DATABASE: flexiuy104_wpi
PERCH_DB_PREFIX: perch2_
PERCH_TZ: Europe/Amsterdam
PERCH_EMAIL_FROM: info@flexiflyer.nl
PERCH_EMAIL_FROM_NAME: Edwin Venhorst
PERCH_LOGINPATH: /perch
PERCH_PATH: /home/flexiuy104/domains/wpizevenaar.nl/public_html/perch
PERCH_CORE: /home/flexiuy104/domains/wpizevenaar.nl/public_html/perch/core
PERCH_RESFILEPATH: /home/flexiuy104/domains/wpizevenaar.nl/public_html/perch/resources
PERCH_RESPATH: /perch/resources
PERCH_HTML5: 1
PERCH_RUNWAY:
PERCH_ERROR_MODE: DIE
PERCH_DATE_LONG: %d %B %Y
PERCH_DATE_SHORT: %d %b %Y
PERCH_TIME_SHORT: %H:%M
PERCH_TIME_LONG: %H:%M:%S
PERCH_RUNWAY_ROUTED:
PERCH_STRONG_PASSWORDS:
PERCH_DEBUG:
PERCH_PREVIEW_ARG: preview
PERCH_TEMPLATE_PATH: /home/flexiuy104/domains/wpizevenaar.nl/public_html/perch/templates
PERCH_DEFAULT_DOC: index.php
PERCH_DEFAULT_EXT: .php
PERCH_PRODUCTION_MODE: 100
PERCH_RWD:
PERCH_HTML_ENTITIES:
PERCH_SSL:
PERCH_STRIPSLASHES:
PERCH_PROGRESSIVE_FLUSH: 1
PERCH_PARANOID:
PERCH_FORCE_SECURE_COOKIES:
PERCH_PASSWORD_MIN_LENGTH: 6
PERCH_MAX_FAILED_LOGINS: 10
PERCH_AUTH_LOCKOUT_DURATION: 1 HOUR
PERCH_VERIFY_UPLOADS:
PERCH_AUTH_PLUGIN:
PERCH_DB_CHARSET: utf8
PERCH_DB_PORT:
PERCH_DB_SOCKET:
PERCH_SESSION_TIMEOUT_MINS: 20
HOSTING SETTINGS

PHP: 5.5.38
Zend: 2.5.0
OS: Linux
SAPI: apache2handler
Safe mode: not detected
MySQL client: mysqlnd 5.0.11-dev - 20120503 - $Id: 15d5c781cfcad91193dceae1d2cdd127674ddb3e $
MySQL server: 5.6.29
Free disk space: 0,00
Extensions: Core, date, ereg, libxml, openssl, pcre, sqlite3, zlib, bcmath, calendar, ctype, curl, dom, hash, fileinfo, filter, ftp, gd, gettext, SPL, iconv, session, intl, json, mbstring, mcrypt, standard, mysqlnd, mysqli, mysql, PDO, pdo_mysql, pdo_sqlite, Phar, posix, Reflection, imap, SimpleXML, soap, sockets, exif, tokenizer, xml, xmlreader, xmlwriter, xsl, zip, apache2handler, mhash, ionCube Loader, Zend Guard Loader
GD: Yes
ImageMagick: No
PHP max upload size: 64M
PHP max form post size: 64M
PHP memory limit: 256M
Total max uploadable file size: 64M
Resource folder writeable: Yes
Session timeout: 24 minutes
Native JSON: Yes
Filter functions: Yes
Transliteration functions: Yes
UNIQUE_ID: WLGJnZ-9B@AAAFFRfHkAAAAD
HTTP_HOST: www.wpizevenaar.nl
HTTP_COOKIE: PHPSESSID=d2772aaced28622081b677018db091ec; cmsa=1; _ga=GA1.2.263211357.1484830876
HTTP_CONNECTION: keep-alive
HTTP_UPGRADE_INSECURE_REQUESTS: 1
HTTP_ACCEPT: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
HTTP_USER_AGENT: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_1) AppleWebKit/602.2.14 (KHTML, like Gecko) Version/10.0.1 Safari/602.2.14
HTTP_REFERER: https://www.wpizevenaar.nl/perch/core/settings/diagnostics/
HTTP_ACCEPT_LANGUAGE: nl-nl
HTTP_ACCEPT_ENCODING: gzip, deflate
PATH: /usr/local/bin:/usr/bin:/bin
SERVER_SOFTWARE: Apache/2
SERVER_NAME: www.wpizevenaar.nl
SERVER_ADDR: 159.253.7.224
SERVER_PORT: 80
REMOTE_ADDR: 46.129.49.97
DOCUMENT_ROOT: /home/flexiuy104/domains/wpizevenaar.nl/public_html
REQUEST_SCHEME: http
CONTEXT_DOCUMENT_ROOT: /home/flexiuy104/domains/wpizevenaar.nl/public_html
SERVER_ADMIN: webmaster@wpizevenaar.nl
SCRIPT_FILENAME: /home/flexiuy104/domains/wpizevenaar.nl/public_html/perch/core/settings/diagnostics/index.php
REMOTE_PORT: 61417
GATEWAY_INTERFACE: CGI/1.1
SERVER_PROTOCOL: HTTP/1.1
REQUEST_METHOD: GET
QUERY_STRING: extended
REQUEST_URI: /perch/core/settings/diagnostics/?extended
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php
PHP_SELF: /perch/core/settings/diagnostics/index.php
REQUEST_TIME_FLOAT: 1488030109,28
REQUEST_TIME: 1488030109