encodeHeader() fell back to us-ascii for any header value without 8-bit
chars, which mislabelled ISO-2022-JP text. Values containing ESC escape
sequences now keep the message charset.
Fixes#2185
mailSend() joined the To addresses for mail() with its own implode, so
a long list still went out as one line, while the To header used for
getSentMIMEMessage() and DKIM signing is folded by addrAppend(). mail()
keeps CRLF + space folds in its to argument, so build it with
addrAppend() too.
If the connection is closed in the middle of a DATA command, for example
from a destructor after SIGTERM, the server takes QUIT as part of the
message and the connection only ends when it times out. SMTP now keeps
the last command it sent in a state property, and quit() just closes the
connection when that command is DATA, as discussed in #3121.
Fixes#2994
addrAppend() joined all addresses onto one line, so a To, Cc, Bcc or
Reply-To header with many recipients could go past the 998 character
limit in RFC 5322. Fold between addresses when the next one would not
fit. Short lists are unchanged.
Fixes#2690
openssl_pkcs7_sign() returns its headers and body with bare LF line
breaks. They were copied into the message verbatim, so signed mail was
rejected by SMTP servers that enforce RFC 5321 line endings with
550 5.6.11 SMTPSEND.BareLinefeedsAreIllegal.
Fixes#3067
dualfroz