<p>The error ‘<em>Handshake failed … SSLV3_ALERT_ILLEGAL_PARAMETER …</em>’ is either caused by a bug in the SSL protocol implementation or by a too short DH key on the email server and can unfortunately not be fixed by FairEmail.</p>
<p>The error ‘<em>Handshake failed … HANDSHAKE_FAILURE_ON_CLIENT_HELLO …</em>’ might be caused by the provider still using RC4, which isn’t supported since <ahref="https://developer.android.com/about/versions/nougat/android-7.0-changes.html#tls-ssl">Android 7</a> anymore.</p>
<p>The error ‘<em>Handshake failed SSL handshake terminated … SSLV3_ALERT_HANDSHAKE_FAILURE … HANDSHAKE_FAILURE_ON_CLIENT_HELLO</em>’ can be caused by <ahref="https://issuetracker.google.com/issues/37122132">this Android 7.0 bug</a>. This can unfortunately not be fixed by FairEmail.</p>
<p>The error ‘<em>Handshake failed … UNSUPPORTED_PROTOCOL or TLSV1_ALERT_PROTOCOL_VERSION or SSLV3_ALERT_HANDSHAKE_FAILURE …</em>’ might be caused by enabling <strong>hardening connections</strong>, or requiring TLS 1.3 in the connection settings or by Android not supporting older protocols anymore, like SSLv3.</p>
<p>The error ‘<em>Handshake failed … UNSUPPORTED_PROTOCOL or TLSV1_ALERT_PROTOCOL_VERSION or SSLV3_ALERT_HANDSHAKE_FAILURE …</em>’ might be caused by enabling <strong>hardening connections</strong> or <strong>Bouncy Castle</strong> in the connection settings tab page, or by Android not supporting older protocols anymore, like SSLv3 and TLSv1.</p>
<p>Android 8 Oreo and later <ahref="https://developer.android.com/about/versions/oreo/android-8.0-changes#security-all">do not support</a> SSLv3 anymore. There is no way to workaround lacking RC4 and SSLv3 support because it has completely been removed from Android (which should say something).</p>
<p>Please <ahref="https://developer.android.com/reference/javax/net/ssl/SSLSocket">see here</a> for an overview of supported protocols and cipher suites by Android version.</p>
<p>You can use <ahref="https://ssl-tools.net/mailservers">this website</a> or <ahref="https://www.immuniweb.com/ssl/">this website</a> to check for SSL/TLS problems of email servers.</p>