"Invalid characters in atom" when squirrelmail plugin connects to managesieve

[Joseph Mays]

I found a similar error to this posted on the dovecot list from 2013, but no 
solution.

I'm using the avelsieve squirrelmail plugin with dovecot. It throws an error 
when it connects to managesieve.

dovecot version is 2.0.19

ngrep of the connection shows....

T 127.0.0.1:4190 -> 127.0.0.1:55753 [AP]
  "IMPLEMENTATION" "Dovecot Pigeonhole".."SIEVE" "fileinto reject envelope en
  coded-character vacation subaddress comparator-i;ascii-numeric relational r
  egex imap4flags copy include variables body enotify environment mailbox dat
  e ihave".."NOTIFY" "mailto".."SASL" "PLAIN LOGIN CRAM-MD5".."VERSION" "1.0"
  ..OK "Dovecot ready."..
##
T 127.0.0.1:55753 -> 127.0.0.1:4190 [AP]
  AUTHENTICATE "PLAIN" \{80+}..
##
T 127.0.0.1:55753 -> 127.0.0.1:4190 [AP]
  bWF5c0A0c2Vhc29uc3Jlc29ydC5jb20AbWF5c0A0c2Vhc29uc3Jlc29ydC5jb20AZmxvdmVyMDk
  xNw==..
##
T 127.0.0.1:4190 -> 127.0.0.1:55753 [AP]
  NO "Invalid characters in atom"..NO "Error in MANAGESIEVE command received
  by server."..