Recommendation for better email software

[#1]

With the following criteria:
Post office hosted on a network drive (NAS)
3 PC's accessing the same mail folder, PC's are in different locations in the buildings.
Single user accessing email can send and receive from any PC.
A Calendar
Outlook works to a fashion but
a) the email accounts need to be set up on each PC, if I change an account it needs to be changed in 3 places.
b) Adding new accounts is a regular occurrence
c) The contacts need to be set up on each PC.
With the cost of hardware getting so in-expensive it is worth considering having 'dual' or 'triple' access to the same email folders.
Online email is currently not a solution as there are 10-12 email accounts feeding into one inbox.

[#2]

With any email client software your going to have the same issues as Outlook.
However,  Thunderbird would allow you to make use of external contacts and calendar systems with some plugins.
It sounds like you need to host your own email server with webmail,  e.g  dovecot and roundcube.
You can even configure plusnet's systems to deliver your email to your server directly.

[#3]

If, when you say single user, you mean a single person not using the email at more than one PC at the same time, then Thunderbird should be able to do this.
There's a bit more detail to the installation but, basically, place the Thunderbird profile folder on the NAS and configure Thunderbird on each PC to look for the profile on the NAS.
The shared profile folder contains all account settings and mail, so account changes need only be actioned once from any PC.
The only restriction should be that Thunderbird can only be accessed from one PC at a time. If you try and access Thunderbird on one PC while Thunderbird is open on another PC, you get stopped with a message telling you that the program is already running.
Does this seem nearer what you want?

[#4]

@kmilburn, think the email server sounds bit of an overkill, but I've an open mind, looking at maximum of 30 emails per day (in) and 30-40 (out)
With my own mail server will I be able to access mail from different PC's.
@Johnj:- sound about right, I've a PC in my workshop, one in my office and a 3rd in the kitchen, the workshop is 50meters from the office and a further 20 meters from the kitchen. Will only be one user, (possibly 2 as SWMBO sometimes uses the same 'inbox'), but it is not really a problem if I get stopped with a message.

[#5]

I've done this for a friend recently, so let me know if you want more details.