Gmail Doesn't Receive Emails Frequently Enough from My External POP3 Email Account

This article from Lifehacker (Make Gmail Check Your POP Accounts More Frequently)
helped me solve an ongoing problem where Gmail was only checking a branded, external email address (POP3 mailbox) about once an hour.  Clients and prospective clients were sending me emails to collaborate on projects and I wasn't receiving anything right away.  Emails were taking 10-60 minutes to be retrieved.

It was frustrating to have to go to Settings > Accounts and Import and manually tell Gmail to fetch more mails from my email address at another domain.

There's also this option in the Labs options section. [source]

Flushing out an Overflowing Gmail Inbox with Targeted Gmail Searches

If you're like me, you may have accumulated dozens of subscriptions that arrive in your inbox daily. Even though it may not seem like much, over months or years, these unread emails can become overwhelming and hard to delete in bulk unless you can find a way to filter them with a search.

Update 4/6/25:

in:inbox is:unread has:nouserlabels 

Finds everything that is unread and has no user labels. Helpful for collecting and deleting unread, unorganized emails in bulk.

Update 5/4/20:

Two new and improved searches to clear out old messages in Gmail

in:inbox is:unread has:nouserlabels NOT label:important NOT is:starred
(The new key search operator (has:nouserlabels) will hide all messages from the search that have a user assigned label.  I almost always apply either an important label or a personal label to messages that I need to save for future use.)

in:inbox is:read has:nouserlabels NOT label:important NOT is:starred
This will show read messages that still do not have personal labels applied.  These messages are likely ones that were opened, read, and then never deleted.

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Here is the Gmail search phrase I use to find unimportant messages, not from friends, and delete them (usually 99 or 100 at a time).

NOT label:important label:unread in:inbox NOT label:starred

You may want to make a few modifications yourself in case you occasionally received messages not marked as important that include attachments (ie: website backups, quarterly reports, etc).

Hide messages from the search results that have attachments:
NOT has:attachment

NOT from:__________