Introduce header-based preference in sender select

Introduce a header-based preference in sender selection, as proposed
in #771.

In the examples below, assume the accounts are ordered X-Y-Z in the
config file.

Suppose I'm in a conversation, sending mails from account Y. However,
I add my account X to the "CC:" header. If I do not receive any replies
before sending another mail, I want to send it from account Y again,
9 out of 10 times. The old version would prefer account X, because it
lumps all headers in one list and gets a match on account X first.

Suppose I have aliasing in my mailserver, but send mails from several
of these aliases. They are not "aliases" as such, but accounts which
happen to share a mailbox. However, account X is the account where the
mail is ultimately sent to so will always be present in the
"Delivered-To:" header, even if the sender only knows my address for
account Y, which is in the "To:". Obviously, I want any replies to be
sent from account Y, not account X. This is fixed by prioritizing
matches on the "To:" over "Delivered-To:".

The only case which this patch doesn't fix is when somebody replies
in the first situation, adding *both* addresses to the "To:" header.
In this case, however, I would be fine manually editing the proposed
sender address.

1 files changed, 32 insertions, 29 deletions

diff --git a/alot/commands/thread.py b/alot/commands/thread.py
index e5ad72a4..3dff6855 100644
--- a/alot/commands/thread.py
+++ b/alot/commands/thread.py
@@ -61,35 +61,38 @@ def determine_sender(mail, action='reply'):
     # extract list of addresses to check for my address
     # X-Envelope-To and Envelope-To are used to store the recipient address
     # if not included in other fields
-    candidate_addresses = getaddresses(mail.get_all('To', []) +
-                                       mail.get_all('Cc', []) +
-                                       mail.get_all('Delivered-To', []) +
-                                       mail.get_all('X-Envelope-To', []) +
-                                       mail.get_all('Envelope-To', []) +
-                                       mail.get_all('From', []))
-
-    logging.debug('candidate addresses: %s' % candidate_addresses)
-    # pick the most important account that has an address in candidates
-    # and use that accounts realname and the address found here
-    for account in my_accounts:
-        acc_addresses = map(re.escape, account.get_addresses())
-        if account.alias_regexp is not None:
-            acc_addresses.append(account.alias_regexp)
-        for alias in acc_addresses:
-            if realname is not None:
-                break
-            regex = re.compile('^' + alias + '$', flags=re.IGNORECASE)
-            for seen_name, seen_address in candidate_addresses:
-                if regex.match(seen_address):
-                    logging.debug("match!: '%s' '%s'" % (seen_address, alias))
-                    if settings.get(action + '_force_realname'):
-                        realname = account.realname
-                    else:
-                        realname = seen_name
-                    if settings.get(action + '_force_address'):
-                        address = account.address
-                    else:
-                        address = seen_address
+    # Process the headers in order of importance: if a mail was sent with
+    # account X, with account Y in e.g. CC or delivered-to, make sure that
+    # account X is the one selected and not account Y.
+    for candidate_header in ['From', 'To', 'Cc', 'Envelope-To',
+                             'X-Envelope-To', 'Delivered-To']:
+        if realname is not None:
+            break
+        candidate_addresses = getaddresses(mail.get_all(candidate_header, []))
+
+        logging.debug('candidate addresses: %s' % candidate_addresses)
+        # pick the most important account that has an address in candidates
+        # and use that accounts realname and the address found here
+        for account in my_accounts:
+            acc_addresses = map(re.escape, account.get_addresses())
+            if account.alias_regexp is not None:
+                acc_addresses.append(account.alias_regexp)
+            for alias in acc_addresses:
+                if realname is not None:
+                    break
+                regex = re.compile('^' + alias + '$', flags=re.IGNORECASE)
+                for seen_name, seen_address in candidate_addresses:
+                    if regex.match(seen_address):
+                        logging.debug("match!: '%s' '%s'" % (seen_address,
+                                                             alias))
+                        if settings.get(action + '_force_realname'):
+                            realname = account.realname
+                        else:
+                            realname = seen_name
+                        if settings.get(action + '_force_address'):
+                            address = account.address
+                        else:
+                            address = seen_address
 
     # revert to default account if nothing found
     if realname is None: