451 Temporary local problem (Outlook 2003)

[#1]

I occasionally have problems sending e-mails using Outlook 2003 (they've happened on and off over the last few months). The e-mail appears in my sent items, but I immediately get an automatically generated e-mail (one generated by Outlook, not one generated by PlusNet) that says:

Quote

Your message did not reach some or all of the intended recipients.       Subject: ###############       Sent: 31/12/2008 10:17 The following recipient(s) could not be reached:       '###########' on 31/12/2008 10:17             451 Temporary local problem - please try later

I've deleted the subject and recipient's name, but it happens to various recipients, so I doubt it's related to the particular recipient.
I'm sure that I have the SMTP settings correct because they work correctly most of the time.
relay.plus.net
without authentication
port number 25
without an encrypted connection
I know that I could change it to require authentication, but since this isn't officially supported by PlusNet I don't want to do this.
Having searched for an answer on t'internet, it seems that it often caused by DNS problems, but I don't have any problems receiving e-mail or visiting any websites.
I am connected to my router, which is connected to PlusNet, so the PlusNet SMTP servers shouldn't block my e-mail.
I suppose this could be related to my anti-virus protection (NIS2008), but I don't want to disable it to find out.
Does anybody have any ideas?
Thanks in advance.
Rob
Update:
I've tried sending an e-mail using webmail, and it worked OK. Since webmail uses different servers, this doesn't necessarily mean there's a problem with my PC.
I've disabled my anti-virus protection, and I still have problems sending.
I've tried sending using other PlusNet e-mail accounts, and I get the same error.
I'll reboot my PC, but rebooting my PC hasn't always fixed the problem in the past, I just need to wait for it to start working again.

[#2]

I suggest you try turning off scanning of *outbound* emails in NIS. In my experience (admittedly with older versions) NIS doesn't integrate well with SMTP relays.
It might be wise to restart your computer after changing this setting to ensure it properly takes effect.

[#3]

Thanks for your reply. I've used NIS for years, and only recently had a problem.
I've already tried disabling scanning of outbound e-mails, but this didn't help. However, I enabled it again before rebooting. I'll turn it off permanently, and then reboot.

[#4]

How long is it since your router was restarted? Again no reason why doing that should make any difrerence, but …

[#5]

Rebooting my PC hasn't solved the problem.
I'm not sure when I last rebooted my router, but It's been a while. I'll give that a go.

[#6]

Thanks again for your help.
Unfortunately, rebooting my router hasn't solved the problem.
Does anybody have any more ideas?

[#7]

is it possible to update the ticket with the emails headers please?
this will be really helpful

[#8]

Quote from: Rob

Having searched for an answer on t'internet, it seems that it often caused by DNS problems, but I don't have any problems receiving e-mail or visiting any websites.

Something elese worth trying (in a process of elimination) is flushing the DNS resolver cache:
type ipconfig /flushdns from a command prompt.

[#9]

Have you read Fahrenheit 451?

[#10]

Thanks for your replies. Everything seems to be working OK today, but I'm sure I'll have to revisit this at some point. I think that the likely problem is PlusNet occasionally blocks my domain. The From: and Reply To: e-mail addresses are both set to me@mydomain.co.uk.
RamiDoodle: I don't think there are any internet headers, because the e-mail didn't get to the internet. When I right mouse click and select options, the Internet Headers box is empty.
Waldo: Thanks. I'll try this next time I have the problem.
Axisofevil: No. Is it likely to help solve my problem?

[#11]

Thanks again for your replies. I am having problems sending e-mails again.
I can send e-mails when my From: and Reply To: e-mail addresses are set to either me@myname.plus.com or me@mydomain.me.uk.
I cannot send e-mails when the From: and Reply To: e-mail addresses are set to me@mydomain.co.uk.
This suggests to me that Plus Net is blocking me@mydomain.co.uk, so I will update the ticket that I raised earlier.

[#12]

I don't use Outlook, so I don't know for certain, but can you / have you set up mail logging. Have a look at smtp.log this may help point a finger.

[#13]

I know you said you didn't want to use authenticated SMTP but I suggest trying it for investigation purposes. This requires the main account portal username and password to be provided and is *not* encrypted SSL.
What is at the back of my mind is that unauthenticated send often requires receive first to provide proxy authentication and I'm wondering if that is being missed so that the send is refused.

[#14]

Anotherone : Thanks for the suggestion. I'm afraid I don't know how to view PlusNet's SMTP log.
spraxyt : I was thinking something similar to you, but I don't want to use something that isn't supported as a solution. However, as you pointed out, it's worth considering for investigating the problem.
I've done some more testing, and although I can send e-mails when my From: and Reply To: e-mail addresses are set to either me@myname.plus.com or me@mydomain.me.uk, any e-mails send to me@mydomain.co.uk (no matter where they're sent from) do not arrive.
Based on this, I assumed that PlusNet's Edge Protection (or whatever it's called) is blocking me@mydomain.co.uk. Turning off Edge Filtering has solved the problem, but it's only a temporary solution for two reasons:

• I will end up getting much more spam.


• Any PlusNet users with Edge Protection turned on will not be able to send e-mails to me.

I didn't realise that Edge Filtering was used on outgoing e-mails as well as incoming e-mails, but the CSC Analyst who last dealt with my ticket (27421226) seems to think that it does.
Rob
PS: Please note I am using two different domains - www.robdickson.me.uk and www.robdickson.co.uk. Both are hosted with different companies, so are likely to be treated differently by PlusNet's spam filtering.
Edit:
I'm not getting any e-mails when replies are made to this post, or when a reply is made to my ticket. In my opinion this proves that PlusNet users are not able to send e-mails to my robdickson.co.uk domain.

[#15]

Relating to your last comment, there are other things going on, actually down or off  which may or may not be related ::), I think somebody said the wrong thing in a post on the chat forum and had put the kiss of death on everything!!
Regards smtp.log that's on your own machine, look somewhere like Tools, Options, Maintenance for the setting. If Outlook Express has it I'm sure Outlook must have something similar. The file itself maybe in the same folder as all the other mail folders. It records all the transactions between your machine and the smtp server.