When trying to send an email from Roundcube I get:

Connection failed: Failed to connect socket: fsockopen(): unable to connect to ssl://mail.covisp.net:587

Sending from any other mail client works on the submission port, so it is not a mail server configuration issue.

If I change it to tls://mail.covisp.net I get:

SMTP Error in /usr/local/www/roundcube/program/lib/Roundcube/rcube.php (1675): Authentication failure: STARTTLS failed (Code: )

$ openssl s_client -connect mail.covisp.net:587 -starttls smtp CONNECTED(00000003) depth=1 C = US, O = Let's Encrypt, CN = Let's Encrypt Authority X3 verify error:num=2:unable to get issuer certificate issuer= O = Digital Signature Trust Co., CN = DST Root CA X3

Certificate chain 0 s:/CN=covisp.net i:/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3 1 s:/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3 i:/O=Digital Signature Trust Co./CN=DST Root CA X3

Server certificate -----BEGIN CERTIFICATE----- MIIGXDCCBUSgAwIBAgISA8l2HqqZkKGc4w829muF4nnZMA0GCSqGSIb3DQEBCwUA MEoxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MSMwIQYDVQQD ExpMZXQncyBFbmNyeXB0IEF1dGhvcml0eSBYMzAeFw0xODAyMTMyMDIxMjZaFw0x ODA1MTQyMDIxMjZaMBUxEzARBgNVBAMTCmNvdmlzcC5uZXQwggIiMA0GCSqGSIb3 DQEBAQUAA4ICDwAwggIKAoICAQCjK35UbUb6YSMSzto4KgLPGv/h8jvkRMYuV3al iV28dXMEPUJ8vhGsLbXaMVKouZnrWMgJ7ws6TlzXNPuMnXuoplvhLMtXNKyAtyaI X0Hhhsb3yAfj2WI7FN15kedKnGFzNPDBuo8+g6q0yRgyj1erNj/K8xWwokpcpVrU Q5zsKnyqU9MHmmcyNFNFyCQ+quCfCLcK4T1klrQGKG564HQcj0hEXFZx6txj7irF Zul/0Ju2XdDaaF114+Fq2K/XCuRWfyWAGTSh8z7e/4CU0MDnnqIAVWcWfeeHLjTU 2hRd7TQEH0DWg1C95zHk0yLn2JJ/ffj0q/+RK8G8yjKogv351VNgfjbkoCxnluFS lYx5IPUdRvplEWOEMdtcvLf7J+S+e+Kf3u643SMKwblOboA9yqWyIrp32voxCWoF kVkO84E70U1yCZ4rbVcF9CwEySi/1la7Nm7Bnr24ByJT46TBlAKPEwUaj0VJeHi4 oHxXAZ3IYjdMgbT+DPWiz/jCrdahQrJC++HFaoqLd+dPGlla3Rn/FjigpABqJUJj YNLAXwP2hY2W1bRdJDjBG7978Uy8h2Ec8TTBjOSIHgQOoxFyuPg+kCinELPFxXmI +kxrtwpKelnxHpH5JdFDLIHN80TAqr5v2CnMA+9JSOjX6z6Yvpwom9LWJ9z34vpn X77OjQIDAQABo4ICbzCCAmswDgYDVR0PAQH/BAQDAgWgMB0GA1UdJQQWMBQGCCsG AQUFBwMBBggrBgEFBQcDAjAMBgNVHRMBAf8EAjAAMB0GA1UdDgQWBBRsPUj9me0H 2wqRgbnPiD2RIYvPUzAfBgNVHSMEGDAWgBSoSmpjBH3duubRObemRWXv86jsoTBv BggrBgEFBQcBAQRjMGEwLgYIKwYBBQUHMAGGImh0dHA6Ly9vY3NwLmludC14My5s ZXRzZW5jcnlwdC5vcmcwLwYIKwYBBQUHMAKGI2h0dHA6Ly9jZXJ0LmludC14My5s ZXRzZW5jcnlwdC5vcmcvMHoGA1UdEQRzMHGCCmNvdmlzcC5uZXSCD21haWwuY292 aXNwLm5ldIIVcGhwbXlhZG1pbi5jb3Zpc3AubmV0ghdwb3N0Zml4YWRtaW4uY292 aXNwLm5ldIISd2VibWFpbC5jb3Zpc3AubmV0gg53d3cuY292aXNwLm5ldDCB/gYD VR0gBIH2MIHzMAgGBmeBDAECATCB5gYLKwYBBAGC3xMBAQEwgdYwJgYIKwYBBQUH AgEWGmh0dHA6Ly9jcHMubGV0c2VuY3J5cHQub3JnMIGrBggrBgEFBQcCAjCBngyB m1RoaXMgQ2VydGlmaWNhdGUgbWF5IG9ubHkgYmUgcmVsaWVkIHVwb24gYnkgUmVs eWluZyBQYXJ0aWVzIGFuZCBvbmx5IGluIGFjY29yZGFuY2Ugd2l0aCB0aGUgQ2Vy dGlmaWNhdGUgUG9saWN5IGZvdW5kIGF0IGh0dHBzOi8vbGV0c2VuY3J5cHQub3Jn L3JlcG9zaXRvcnkvMA0GCSqGSIb3DQEBCwUAA4IBAQBONofC5LjFT2KSgkPjvuus shIprx/VYgOpfgFCvAmkQCbpLp8NmS8r4Dg9mMAqh/uhPgRV6BoGiuBR7eJRKH/W /sOY0AtysFxdslWb0hhCjaTXEGNz8c9z53xslNlU1ggp2k71FVzbFfhKnaDbYwem XXyquK2QKg5yPWxGmsfMSyNuP8q/qHCqBRiOWNxozSHw1k0Qr9cod1748hd/+HG4 nGBUiIQUPEJdWm3b+zvlr0PBKaOC4j3LSQpXj4FvHDy19DxxkmVNEE4+px5B0qJ9 WeXyPb2Hop4Ly6o9UKaynICgYEC2CXrRv7GZ/oGesdpF7k9mEA5Tt1nbW+rp+exF -----END CERTIFICATE----- subject=/CN=covisp.net issuer=/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3

No client certificate CA names sent Peer signing digest: SHA512 Server Temp Key: ECDH, P-256, 256 bits

SSL handshake has read 3783 bytes and written 468 bytes

New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384 Server public key is 4096 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE No ALPN negotiated SSL-Session: Protocol : TLSv1.2 Cipher : ECDHE-RSA-AES256-GCM-SHA384 Session-ID: 41E4C231E6E193E6DAC1CFBA6C890132BD10B24467F056BEBB68BEE0D5D2E275 Session-ID-ctx: Master-Key: E40F4A64F059BE52089D0F1F5CCF7E0640C870C618FA4FB97337AF1ED43F4F3A325610088EC67BCB2C5113E5E7CC3D9B Key-Arg : None PSK identity: None PSK identity hint: None SRP username: None Start Time: 1519428085 Timeout : 300 (sec) Verify return code: 2 (unable to get issuer certificate)

250 DSN