It is not uncommon for one to have more than one webmail account. You might have a Gmail and also a Yahoo! Mail account as required in order to access services from both Google and Yahoo!. Or you might have a personal Gmail account and also one for business.
Gmail, Yahoo! Mail, Outlook.com etc webmail accounts all require you to sign in to your account within a period in order to keep the account alive. This account inactivity grace period varies by webmail provider.
If you have few number of webmail accounts, it’s no brainer to sign in to your webmail accounts within the account inactivity period. If you have dormant email accounts or are managing far too many webmail accounts, then it becomes a tiresome routine to sign in to each webmail account one-by-one.
You can “automate” the account sign in chore by using a local mail client such as the Mail app that comes with OS X or Mail for iOS. Some webmail provider such as Gmail requires settings changes before you can access your mails via a local mail app. For Gmail, go to its settings page at gmail.com. Click on Forwarding and POP/IMAP tab and check the option Enable IMAP.
Setup all your webmail accounts in Mail app. Thus when Mail app is run on your Mac or on your iPhone, it will sign in automatically to all your webmail accounts, thus keeping all accounts up-to-date.