Think that soft bounces are caused by a full inbox? Then think again!

Think that soft bounces are caused by a full inbox? Then think again!

Dela Quist
Alchemy Worx

Most email marketers do not view soft bounces as being a major cause
for concern, so rarely, if ever, have any specific strategies been in
place for dealing with them. Soft bounces are a very strong indication
that one or more ISPs were concerned enough about the reputation of the
IP address you are using,  your mailing volumes or the level of SPAM
complaints you are generating to temporarily block your campaign.

Over
the last two years our agency has begun to take soft bounces very
seriously indeed. Compared with soft bounces, hard bounces are
relatively straight forward – there are far fewer reasons for their
occurrence and only one way of dealing with them, which is to remove
them from your list.

The reason so many people
don’t treat soft bounces seriously enough seems to be because most
definitions of a soft bounce are outdated.  

Here are but two typical examples of the definition of a soft bounce taken from well respected sources:

• A
  soft bounce just means the recipient's email account was 'temporarily
  unavailable'. Maybe their server was busy, or the recipient was away on
  vacation, or their account was too full.

• A
  soft bounce occurs when the recipient's mail server replies with an
  error other than 5xx, or never replies at all. An example of a soft
  bounce error could be caused by a server that overloaded or a user
  whose mailbox is full.

Most
current definitions of a soft bounce do not really convey any sense of
urgency or importance, worst of all they seem to indicate that the
bounce had nothing to do with your mail marketing practice at all.
After all what can you do to stop someone’s server crashing or being
taken down for maintenance or a subscriber’s mailbox filling up while
they are on holiday?

Some ESPs set the default for
removing soft bounces at 10 or more and best practice guidelines
typically suggest removal after 3 subsequent bounces, further reducing
the sense of urgency.

General definitions of a soft bounce and guidelines for dealing with them haven’t changed for at least five years!

In
this time inbox sizes have dramatically increased so 'mailbox full'
messages are highly unlikely to occur; Gmail currently offer 7GB of
storage! I don’t know anyone who has exceeded their Gmail or for that
matter Yahoo or Hotmail storage limit and even if there are such
people, they are hardly representative of the average consumer. Even if
you have a large number of people using their work email address, how
many companies start bouncing potentially valuable communications
without letting the user know that their inbox is due a spring clean.

I
also suspect that bounces caused by overloaded ISPs (Hotmail etc.) or
corporate servers are not as common as the definitions quoted above
would seem to indicate.

This means that the most likely cause of soft bounces is ISP blocking.

The
way ISPs deal with spam has become much more aggressive and incredibly
sophisticated. For a start they are very quick to start blocking emails
when they identify suspicious patterns of behaviour from a given
sender, IP address or range.

Typical causes of
blocking are: lack of authentication or accreditation; poor or unproven
IP reputation; fluctuations in the volume of messages sent from the IP
address you are using and spam complaints attributed to your IP
address. It's important to bear in mind that you may incur soft bounces because of the behaviour of companies sharing your IP address, making the way your ESP handles its shared IP addresses very important.

Emails blocked in this way are recorded as soft bounces, so your soft
bounces are important indicators of how 'Spammy' ISP’s think you are at
a given point in time. They
are an indication of a drop in reputation for the IP address you are
using, uneven mailing patterns and/or an increase in the level of SPAM
complaints your email is generating.  All of these things are things that you and your ESP can do something about!

The purest definition of a soft bounce is 'A delivery failure with a 4XX/Transient bounce code' examples of which are:

• 421 Grey listing = Re-try now and send again

• 451 no reverse DNS = Re-try now and send again later after you fix your DNS

Soft bounces should be regularly investigated because we believe that they are more likely to be caused by temporary ISP blocking than temporary problems related to individual subscribers.

I
would strongly recommend that anyone wanting to get a better
understanding of where soft bounces fit in the overall scheme of
deliverability should read the excellent 4 part series of articles on 'How Email Works' by Dennis Dayman of Eloqua

-Dennis
Eloqua

Don't Just Send, Deliver!

Last 5 posts by Dennis Dayman

• Delivery and deliverability debunked - May 7th, 2012
• European Regulator Warns Silicon Valley About Privacy - April 28th, 2012
• Canada’s anti-spam law won’t take effect until 2013 - April 28th, 2012
• Mr. Dayman Goes to Washington - April 2nd, 2012
• EU proposes a reform of the data protection rules - March 28th, 2012