Hmm, even with dropbox and google drive turned off the problem reappeared when going from work to home again. This is the log from the connection doctor. The offending accounts (red dots) are imap.gmail.com and imap.hubrussel.be:
INITIATING CONNECTION Oct 03 22:27:22.097 -- host:imap.gmail.com -- port:993 -- socket:0x0 -- thread:0x7fd3ace292b0
INITIATING CONNECTION Oct 03 22:27:22.098 -- host:in.base.be -- port:110 -- socket:0x0 -- thread:0x7fd3ace7eac0
INITIATING CONNECTION Oct 03 22:27:22.098 -- host:smtp.gmail.com -- port:587 -- socket:0x0 -- thread:0x7fd3af30c610
INITIATING CONNECTION Oct 03 22:27:22.098 -- host:imap.hubrussel.be -- port:143 -- socket:0x0 -- thread:0x7fd3af3ca170
INITIATING CONNECTION Oct 03 22:27:22.098 -- host:in.base.be -- port:110 -- socket:0x0 -- thread:0x7fd3af4a3120
INITIATING CONNECTION Oct 03 22:27:22.098 -- host:out.base.be -- port:25 -- socket:0x0 -- thread:0x7fd3ac5406c0
CONNECTED Oct 03 22:27:22.173 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
CONNECTED Oct 03 22:27:22.176 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
CONNECTED Oct 03 22:27:22.179 [kCFStreamSocketSecurityLevelNone] -- host:out.base.be -- port:25 -- socket:0x7fd3aae11320 -- thread:0x7fd3ac5406c0
CONNECTED Oct 03 22:27:22.186 [kCFStreamSocketSecurityLevelNone] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
READ Oct 03 22:27:22.207 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
+OK Dovecot ready.
WROTE Oct 03 22:27:22.214 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
CAPA
READ Oct 03 22:27:22.218 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
+OK Dovecot ready.
READ Oct 03 22:27:22.232 [kCFStreamSocketSecurityLevelNone] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
220 mx.google.com ESMTP f1sm11105266wiy.2
WROTE Oct 03 22:27:22.249 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
CAPA
READ Oct 03 22:27:22.254 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
+OK
CAPA
TOP
UIDL
RESP-CODES
PIPELINING
STLS
USER
SASL PLAIN LOGIN
.
WROTE Oct 03 22:27:22.276 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
AUTH PLAIN
WROTE Oct 03 22:27:22.278 [kCFStreamSocketSecurityLevelNone] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
EHLO [192.168.1.86]
READ Oct 03 22:27:22.284 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
+OK
CAPA
TOP
UIDL
RESP-CODES
PIPELINING
STLS
USER
SASL PLAIN LOGIN
.
WROTE Oct 03 22:27:22.315 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
AUTH PLAIN
READ Oct 03 22:27:22.317 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
+
READ Oct 03 22:27:22.333 [kCFStreamSocketSecurityLevelNone] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
250-mx.google.com at your service, [94.108.227.48]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS
250 ENHANCEDSTATUSCODES
READ Oct 03 22:27:22.348 [kCFStreamSocketSecurityLevelNone] -- host:out.base.be -- port:25 -- socket:0x7fd3aae11320 -- thread:0x7fd3ac5406c0
220 relay03ant.iops.be ESMTP
READ Oct 03 22:27:22.351 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
+
WROTE Oct 03 22:27:22.357 [kCFStreamSocketSecurityLevelNone] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
STARTTLS
WROTE Oct 03 22:27:22.367 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
************************
WROTE Oct 03 22:27:22.378 [kCFStreamSocketSecurityLevelNone] -- host:out.base.be -- port:25 -- socket:0x7fd3aae11320 -- thread:0x7fd3ac5406c0
EHLO [192.168.1.86]
WROTE Oct 03 22:27:22.386 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
****************************
READ Oct 03 22:27:22.408 [kCFStreamSocketSecurityLevelNone] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
220 2.0.0 Ready to start TLS
READ Oct 03 22:27:22.426 [kCFStreamSocketSecurityLevelNone] -- host:out.base.be -- port:25 -- socket:0x7fd3aae11320 -- thread:0x7fd3ac5406c0
250-relay03ant.iops.be
250-PIPELINING
250-SIZE 20480000
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
WROTE Oct 03 22:27:22.433 [kCFStreamSocketSecurityLevelNone] -- host:out.base.be -- port:25 -- socket:0x7fd3aae11320 -- thread:0x7fd3ac5406c0
EHLO [192.168.1.86]
READ Oct 03 22:27:22.486 [kCFStreamSocketSecurityLevelNone] -- host:out.base.be -- port:25 -- socket:0x7fd3aae11320 -- thread:0x7fd3ac5406c0
250-relay03ant.iops.be
250-PIPELINING
250-SIZE 20480000
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
WROTE Oct 03 22:27:22.492 [kCFStreamSocketSecurityLevelNone] -- host:out.base.be -- port:25 -- socket:0x7fd3aae11320 -- thread:0x7fd3ac5406c0
QUIT
WROTE Oct 03 22:27:22.630 [kCFStreamSocketSecurityLevelTLSv1SSLv3] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
EHLO [192.168.1.86]
READ Oct 03 22:27:22.692 [kCFStreamSocketSecurityLevelTLSv1SSLv3] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
250-mx.google.com at your service, [94.108.227.48]
250-SIZE 35882577
250-8BITMIME
250-AUTH LOGIN PLAIN XOAUTH XOAUTH2
250 ENHANCEDSTATUSCODES
WROTE Oct 03 22:27:22.701 [kCFStreamSocketSecurityLevelTLSv1SSLv3] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
AUTH PLAIN (*** 56 bytes hidden ***)
READ Oct 03 22:27:23.213 [kCFStreamSocketSecurityLevelTLSv1SSLv3] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
235 2.7.0 Accepted
WROTE Oct 03 22:27:23.220 [kCFStreamSocketSecurityLevelTLSv1SSLv3] -- host:smtp.gmail.com -- port:587 -- socket:0x7fd3acb4ccc0 -- thread:0x7fd3af30c610
QUIT
READ Oct 03 22:27:26.729 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
+OK Logged in.
WROTE Oct 03 22:27:26.740 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
QUIT
READ Oct 03 22:27:26.774 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3af524e90 -- thread:0x7fd3ace7eac0
+OK Logging out.
READ Oct 03 22:27:30.698 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
+OK Logged in.
WROTE Oct 03 22:27:30.708 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
QUIT
READ Oct 03 22:27:30.748 [kCFStreamSocketSecurityLevelNone] -- host:in.base.be -- port:110 -- socket:0x7fd3acc96d10 -- thread:0x7fd3af4a3120
+OK Logging out.