Yahoo Groups has a number of functions (commands) that you can use by email, without needing to access Yahoo's web pages. These were once documented in the help system, but for unknown reasons Yahoo removed that help page many years ago, and has apparently not replaced it.
Some of these email addresses are listed on each group's Info/About page, near the bottom, under the heading Group Email Addresses. As used below, groupname is a placeholder for the name of the group involved. See the group's home page or other information for the exact spelling of each group's name (email address).
groupname@yahoogroups.com Post a message. This is the most fundamental activity at any group and uses the base address without a command suffix. Your email message will be forwarded (remailed) to each of the group members. Note: as of 2019-12-16 the moderation feature was removed from most groups. If moderation still applies to your message, either as a group-wide setting or applied to your subscription, your message will be held pending approval by a group moderator.
groupname-owner@yahoogroups.com Send a message to the group moderators and owners. Your message will be forwarded to the moderators and owners of the group. This address may be used by anyone, including non-members.
Using these commands is a two-step process:
The command will not take effect until you complete the second step.
To issue the commands below send a blank message to the command address. The command address is the same as the group's posting address, but with a command appended after the group name in the address. The content of the Subject line and body of your message is ignored.
groupname-subscribe@yahoogroups.com Subscribe to the group. This command adds your email address (the address you send the command from) to the group's Pending Approval list for moderator approval of your application to join the group. Note: as of 2019-12-16 all groups are supposed to have been converted to Restricted membership, if open membership still applies to this group this command will add your email address directly to the group's Membership list. The default subscription is to receive Individual messages as they are posted.
groupname-unsubscribe@yahoogroups.com Unsubscribe from the group. This command removes your email address from the group's membership list.
groupname-nomail@yahoogroups.com Stop receiving messages. This command allows you to suspend delivery of messages to your email address without removing your address from membership in the group. Note that the messages you don't receive are not available for later viewing online; you may wish instead to set a filter in your email interface to store the messages in a folder other than your Inbox.
groupname-digest@yahoogroups.com Switch your subscription to Daily Digests. Daily Digests are sent once per day or at every 15th message, whichever comes first. This can be useful to reduce the number of messages from the group without missing any of the content. Note that Daily Digests are explicitly listed as a feature that is going away in Yahoo's 2019-10-14 notice of what's changing in Yahoo Groups, but as of 2020-01-18 seem to still be working. Use this option at the risk of losing messages when the Digest feature ultimately does stop working. As with No Email, consider using a filter in your email interface as an alternative.
groupname-normal@yahoogroups.com Switch your subscription to Individual Emails. This command restores your subscription to the default delivery of posted message individually as they are received.
groupname-help@yahoogroups.com Receive an automated message about the group. This command causes Yahoo Groups to send you an automated reply containing information about the group. This information is largely taken from the group's home page (Info/About). The group owners and moderators are not notified of your help request.
groupname-traditional@yahoogroups.com Switch your subscription to traditional format. Traditional format refers to the plain text formatting used in Yahoo Groups messages prior to 2006. In this subscription format messages that were posted as plain text (text/plain) are sent to you in plain text, including the Yahoo Group message footers; messages posted in formatted text (text/HTML) are sent to you in that format, including formatted footers. If your subscription is set to Digest the digests you receive will be plain text.
groupname-fullfeatured@yahoogroups.com Switch your subscription to full featured format. Full Featured refers to the formatted text used in Yahoo Groups messages since 2006. In this subscription format messages that were posted as plain text (text/plain) are converted to formatted and a formatted footer applied; messages posted in formatted text (text/HTML) are sent to you in that format, including formatted footers. If your subscription is set to Digest the digests you receive will use formatted text for the header, table of contents, footer, and other structural parts of the digest, but the content of the messages will be presented in plain text (formatting removed).