Re: [Evolution] Errors receiving mail via POP

[Patrick O'Callaghan <poc usb ve>]

On Wed, 2014-09-03 at 18:26 +0100, Pete Biggs wrote:
> On Wed, 2014-09-03 at 10:22 -0600, Zan Lynx wrote:
> > On 9/3/2014 5:45 AM, Pete Biggs wrote:
> > > I've never heard of a problem of IMAP duplicating emails and, knowing
> > > how the protocol works, I can't see how it can!
> >
> > The protocol won't, but servers and clients will.
> >
> > I've had Thunderbird (old version, now fixed) time out while copying 
> > large numbers of email messages from one folder to another. This 
> > resulted in copies of the message in both folders, because it didn't 
> > delete the messages until the copy was complete.
> >
> > I've also had the server lose delete flags on abnormal client shutdown, 
> > which means that messages copied to another folder get resurrected, 
> > resulting in two. And when the filter runs again on next client startup, 
> > more copies are created.
> >
> > So yeah, IMAP can make copies happen.
>
> No, IMAP can't - there's nothing in the protocol specification that
> would lead to a duplication of emails.  The implementation of the
> protocol is a different matter - in fact the problems you mention are
> totally protocol independent.  Bad things can happen when using IMAP but
> they aren't necessarily IMAP's fault.

Any distributed system is subject to partial failure, i.e. one part
stops working or loses communication with another part. If data is in
the process of being moved between the two parts when that happens, the
designer has to decide between allowing data to be lost and opening the
possibility of duplicating it. Systems which aim for reliability
invariably choose the latter option, because the mess can always be
cleaned up later. Sometimes the cleanup is automatic (e.g. transactional
databases, many remote filesystems) and sometimes it's "manual" (i.e.
visible to the end user). AFAIK all email systems fall into the latter
category because a) it's not that big a deal, and b) doing it
automatically would be complicated and could introduce other errors.

poc