The system administrator says he had installed a new certificate the previous day, so that may have had something to do with the problem. Anyway, after a day or so, two of the computers (my home machine and my laptop) spontaneously started being able to connect to the IMAP server again. But my work machine is still throwing this error. Does anyone know how I can troubleshoot this problem? Here is what I have already tried:Error: An error occurred during a connection to mx.ukp.informatik.tu-darmstadt.de:993.
SSL received a record that exceeded the maximum permissible length.
Error code: <a id="errorCode" title="SSL_ERROR_RX_RECORD_TOO_LONG">SSL_ERROR_RX_RECORD_TOO_LONG</a>
- I tried removing the cert8.db and/or cert_override.txt files from my profile before starting Thunderbird. This had no effect.
- I tried copying the cert8.db file from my home machine. This had no effect.
- I tried creating a new profile and adding the IMAP account. Thunderbird won't even let me add the account because it can't connect to the server (but doesn't provide a more specific error message).
- I tried adding the IMAP account with a couple different IMAP clients. KMail also refuses to add the account because can't connect to the server; it throws the error "SSL handshake failed." Evolution has the same problem; its error message is "Error performing TLS handshake: An unexpected TLS packet was received."
- I tried reinstalling my system-wide CA certificates (via my distribution's ca-certificates package). This had no effect.
- I tried using the openssl command-line tool to retrieve the certificates from the server, on both my home machine and my work machine:Apart from the timestamp, session ID, and master key, the output is nearly identical:
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openssl s_client -showcerts -connect mx.ukp.informatik.tu-darmstadt.de:443 </dev/null
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$ diff /tmp/*.crt 117d116 < Server Temp Key: ECDH, P-256, 256 bits 119c118 < SSL handshake has read 5262 bytes and written 427 bytes --- > SSL handshake has read 5262 bytes and written 395 bytes 126d124 < No ALPN negotiated 130c128 < Session-ID: 2D3500005AB2C579E7295DA59102E7D447C4B63D5FB22580A4C0DA6BA341FB58 --- > Session-ID: 6B000000EC3B8A27B25418B0486F8D3BF2E35D02B1B1E1B9B6DA01789BBB4A38 132c130 < Master-Key: CE1755695B0E0114DBB1E5C303177EE57F9A219AE0B52BD44B5D7412789C0DCB4181C4742D58EF0C1F5451CAA8B9335A --- > Master-Key: 3A76D172277BF9060541E54EF5518158BC5204F1ADCC5704A207C91EBBD63C69A73D3766996014E5F327E23A25492A88 137c135 < Start Time: 1484565348 --- > Start Time: 1484565365