The messages you are receiving are broken.  RFC 2369 [3] explicity 
states for List-* Headers: "There MUST be no more than one of each 
field present in any given message."  Errors-to is a non-standard 
header (see RFC 2076), but would not be causing the error you report 
(this error is only triggered by list headers).



I'll go ahead and add a check in MIME_Headers::getValue() to 
explicitly prevent this from happening in the future.

I remember this too. What Horde version are you using?

I have a feeling this was fixed at some point, but I can't find the 
fix or a ticket...

I see this notice when opening some email messages in IMP H3 4.0.3 
(and previous too):



Notice: Array to string conversion in 
/www/webapps/htdocs/monbureau-v3/imp/lib/MIME/Headers.php on line 75



I tracked down the problem to messages having multiple copies of the 
same headers like "Errors-to:" or Lists headers like "List-Owner:" 
etc. (This happens for example when a list address is a member of 
another list, so the mail passes through two lists and have the 
headers of each list).



Displaying all headers show a lot of theses "Notice:"  messages but 
all copies of headers are shown correctly (preceded by list bullets). 
When showing list info headers, "Notice" messages also show, and 
headers with multiple entries simply show as "Array".



Not a big deal since it's a pretty rare situation, but maybe it is 
simple to solve?



Thanks.



Luc.