Unofficial Troubleshooting Guide:

Introduction. Sometimes people have trouble sending, seeing and 
receiving their messages in Google Groups. This unofficial 
troubleshooting guide gives some tips on how you might be able solve 
those problems.

Reporting a problem. If you report a problem on the Google Groups 
forum about having trouble sending and seeing your messages, some 
information might help the group regulars or Google employees to 
figure out the problem, so you might want to tell the following 
information: Can you or anyone else post or see messages sent to a 
particular group? Are you using an email client program (for example 
Outlook Express, Mozilla Thunderbird, etc.) or an email service (for 
example Gmail, Hotmail, Yahoo! Mail, etc.) to email the messages. Or 
are you using the Google Groups web interface to post messages? If you 
are using the Google Groups web interface, which web browser are you 
using (for example Internet Explorer, Mozilla Firefox, Opera, etc.)? 
Do you get any error messages, and if so, what are they exactly?

Emailing messages. If you send an email message to the email address 
of a group, check that you send that email message from an email 
address that is used as a member (or manager or owner) of that group. 
Also, check that the group email address is correct. If you are using 
file attachments, make sure that the size of the email message 
(including the file attachments) is no more than 1 MB in size (which 
seems to be the current size limit at the moment). File system and 
encoding issues may lower the actual size limit of a message 
(including file attachments). If you are trying to send a simple small 
email message with no file attachments, then maybe there is something 
wrong with your email service provider or your internet service 
provider. Sometimes email service provider may block email messages 
from a certain internet domain if a lot of spam messages are sent from 
that internet domain. If you are using an email client program or an 
email service, check it's settings. If you are using a 
forwarding/vacation setting or a spam filter with your email client 
program/service, that can cause problems, so check your spam/junk mail 
box and also the email address you are using to forward your messages 
to/from. Security software such as firewalls may prevent you from 
sending email messages, so check the settings of your security 
software. If you are trying to send email from work, maybe there is a 
computer/company firewall or other settings that do not allow you to 
send email messages with every email service to every internet domain, 
in which case you may need to contact the system/network 
administrator.

Posting messages using the Google Groups web interface. If you are 
using the correct email address, make sure the email address you are 
using is a member/manager/owner of that group. Make sure the email 
address you are using is not moderated, removed (unsubscribed) or 
banned. To see the settings for the email address you are using with a 
group, go to the main page of that group and sign in to Google Groups 
(if you haven't already). Then look on the right hand side of the 
page. If you see a link "Join this group" then you probably are not a 
member of that group, so click that link to join that group. If you 
are a manager or owner of that group, then click the "Management 
tasks" link. Then click the "Manage members" link. Search for the 
email address you are using (the search box should be at the bottom of 
the page next to the "Find member" button, which you need to click 
after you have typed the email address). Click the "Edit" link on the 
same line that mentions your email address. If the setting is 
"Member's posts are moderated" then you are moderated and you need to 
approve each message you post. If the setting is "Member is not 
allowed to post" then you can not post messages. Change the setting to 
"Member is allowed to post" if you want to post messages and without 
being moderated.

Check the group settings. If you are the manager or owner of the 
group, go to the main page of that group, sign in to Google Groups (if 
you haven't already), click the "Group settings" link on the right 
hand side of the page. Click the "Access" link quite at the top of the 
page. If the setting "Who can post messages?" is "Managers only" then 
only managers can post to that group. If you are using the setting 
"All messages are held for moderation" then all messages need to be 
approved first. Now click the "Email delivery" link quite at the top 
of the page. If the setting "Replies are sent to the whole group" is 
not used, then your group might not receive any messages.

Check the settings of the members of the group. If you are the manager 
or owner of the group, go to the main page of that group, sign in to 
Google Groups (if you haven't already), click the "Management tasks" 
link on the right hand side of the page. Click the "Manage members" 
link quite at the top of the page. Look at the "Delivery" column. If 
the setting is "No Email" then person will not receive messages 
emailed or posted to that group. When you invited/added that member 
you may have used other than the "No Email" setting, but each member 
of the group may change their delivery settings if they wish to do so.

Other members. If a group has many managers, maybe one of them has 
changed some critical settings in the group, so check the group 
settings mentioned above. Or maybe a manager has accidentally changed 
the email delivery settings for a member or even removed/banned that 
member, so the check the settings for a member who has problems in 
sending, receiving or seeing messages.

Moderated group. If the group is moderated (uses the "All messages are 
held for moderation" setting), your messages won't appear until the 
group owner or manager approves your messages. All the managers of the 
group may be on a vacation, in which case it may take days or even 
weeks before anyone checks the moderation queue of the group and 
approves messages. One possibility is that a manager may have 
accidentally removed your messages and if you suspect that is the 
case, then you might want to contact the group owner of the group by 
going to the main page of the group and by clicking the "About this 
group" link and then the "Send email to the owner" link (or send email 
to the group address, which should be shown on that "About" page).

Private group. If the group is private (uses the "Only members can 
view group content" setting), then only members who are signed in can 
view the contents of the group using the Google Groups web interface.

Invitation-only group. If the group is invitation-only group (uses the 
"People have to be invited" or "People can request an invitation to 
join" setting) you need to be invited to that group (and then you need 
to accept that invitation) before you can post messages to that group.

Automatic spam filtering. Sometimes the automatic spam filtering 
system in Google Groups marks some messages as "Message may be spam" 
so if you are the manager or owner of the group, go to the main page 
of that group, sign in to Google Groups (if you haven't already), 
click the "Management tasks" link, click the "Review pending messages" 
and see if your message is in the moderation queue.

Invited and added members. If a person who is trying to post a message 
has been invited to the group by using the group's invitation 
function, that person needs to accept the invitation before that 
person begins to receive messages emailed or posted to the group. If a 
person has accepted the invitation to the group or has been added to 
the group, that person may post messages to the group via email but if 
that person wants to post messages to the group using the Google 
Groups web interface, that person needs to create a Google account for 
that person's current email address to be able to post messages using 
the Google Groups web interface. If a person who has been tried to be 
invited/added to a group already has a Google account, that person 
might be using the Google Groups settings "Do not allow group managers 
to invite me to their groups" and "Do not allow group managers to 
directly add me to their groups" in which case that person can not be 
invited or added to the group and he will not receive messages emailed 
or posted to the group, because only group members can receive 
messages sent to the group.

Problems in Google Groups. If Google Groups servers have problems, 
sometimes it can take hours or even days for some or all the messages 
to appear to the discussion section of the group and emailed to the 
group members. You may need to post the same message again if you see 
for example a "Server Error" or "Oops" (or similar) message when you 
are using the Google Groups web interface to post a message. With any 
discussion service it's wise to save your messages to a text file 
before pressing the "Post message" (or similar) button, in case the 
discussion service is encountering problems, your internet connection 
disconnects, your web browser hangs, etc.

Gmail's Inbox. Gmail has a feature where you might not see your 
messages in your Inbox if you have sent messages to yourself or to a 
discussion service:

"Mail you send or forward to a mailing list you subscribe to, or to an 
account that forwards messages to your Gmail account, will only appear 
in 'Sent Mail.' This is intended to help prevent clutter in your 
inbox. If a message isn't successfully delivered, you'll receive an 
error message in your inbox."
http://mail.google.com/support/bin/answer.py?answer=10314

Cookies and cache. Sometimes cookies get corrupted and cause problems 
when using the Google Groups web interface, so try deleting your 
cookies for Google. Your web browser's cache may be full and cause 
problems, so try emptying your browser cache:

http://www.google.com/support/bin/answer.py?answer=497&topic=8998
 

See also these help pages:

http://groups.google.com/support/bin/answer.py?answer=46491&topic=9253
http://groups.google.com/support/bin/answer.py?answer=46490&topic=9253
http://www.google.com/support/bin/answer.py?answer=502

If the above instructions didn't help, then it might be a bug in 
Google Groups. If you don't want to mention your group in the forum 
(so other people can take a look at it), contact the Google Groups 
team using the below feedback form:

http://groups.google.com/support/bin/request.py

P.S. Google's services have the habit of changing, so for example the 
text used in the links mentioned above may change or the help pages 
mentioned above may disappear, so the above instructions may be partly 
or entirely outdated in the future.