Known symptoms when archiving Yahoo mailboxes
Posted by on 14 May 2019 12:37

(1) Yahoo mail settings regarding MailStore

IMAP is the best way to connect your Yahoo Mail account to a desktop mail client or mobile app. It allows 2-way syncing, which means everything you do remotely is reflected in your Yahoo Mail account no matter where or how you access it. Here are the settings you'll need to configure your mail client or app.
Please note IMAP server settings for Yahoo Mail ( )


Incoming Mail (IMAP) Server:

Server -
Port - 993
Requires SSL - Yes

Incoming Mail (POP) Server:

Server -
Port - 995
Requires SSL - Yes

Your Login Info:

Email address - Your full email address (
Password - Your account's password
Requires authentication - Yes


(2) Yahoo known issues regarding MailStore

(a) Symptom/Error:

The archiving process with an Yahoo-mailbox is interrupted and MailStore Home is returning the IMAP error message: “The IMAP Server has returned an error”. In addition, you may see one of the following messages together with the error message:

  • UID FETCH Temporary failure onserver [CODE: WBL] (NO).
  • UID FETCH Server error whilefetching messages (NO).
  • UID FETCH Server error -Please try again later (NO).
  • UID FETCH Rate limit hit (NO).


  1. In order to successfully archive a Yahoo mailbox or emails from another provider, the archiving process may need to be started several times until no more error messages appear. Already archived emails will be recognized and skipped.  After the process has run a number of times the entire contents will be archived.
  2. In case this does not help, you should set up multiple archiving profiles, where each profile archives only a part of the folder structure. This way the total number of emails to be archived is split into smaller parts that then require less time.
  3. In addition folders with large amounts of emails should be split into smaller folders.

 This will reduce the folder sizes and speed up the archive time.


This is a known error message when you are trying to archive from a Yahoo Mailbox. This message can occur seen when the archiving profile has been running for exactly one hour. Unfortunately, Yahoo tends to slow down the client connection for IMAP and POP3, with random error messages. When using MailStore Home this may lead to an error or a cancellation of the archiving for the folder currently being processed or the archiving continues at a reduced speed.

(b) Symptom/Error:

If an error message occurs: “An error has occurred” a connection attempt failed because the connected party did not properly respond after a specific time, or an established connection failed because the connected host failed to respond. Or if you are prompted for a password or username  error message: AUTHENTICATIONFAILED (#MBR1213) Please verify your account by going to (NO) occurs


Yahoo provides the following help: Please read the article from Yahoo “Ways to securely access Yahoo Mail” on the website ( )

Options to securely access Yahoo Mail (as of January 2018)

  • Use the Yahoo Mail website:
  • Install the Yahoo Mail app on your Android or iOS devices
  • Update or upgrade to the latest version of the third-party email app that you want to use
  • Give temporary access to outdated third-party apps
  • While you switch apps or update your app, you can give the old app temporary access. Just remember, this is not intended for permanent access and you'll want to turn it off afterwards
  • Sign in to Yahoo Mail
  • Go to your "Account security" settings
  • Turn on Allow apps that use less secure sign in
    • Once the feature is turned on, you'll get regular alerts reminding you to turn it off. To do so, just follow the steps above and turn off "Allow apps that use less secure sign in."


By default, Yahoo blocks access to Yahoo Mail from several third party apps that could leave your account vulnerable. If Yahoo sents you an email indicating that your app is using outdated security protocols or you're unable to log in from an older app, you still have several options listed above available to you.


(c) Symptom/Error:

Errors appear with the following,  message size limits exceeded


There are several approaches to work around this symptom. Yahoo has documented information on its website, which is listed below.
Message size limits in Yahoo Mail ( )
Yahoo lets you send and receive emails up to 25MB. The total size, including all attachments and encoding, must be below this limit. Keep in mind, encoding can be about a 3rd of the attached file size.

Additional Information:

Yahoo restrictions and limitations:  Limits on sending email in Yahoo Mail ( )

In order to better enforce anti-spam policies, Yahoo does not disclose the number of recipients or emails that can be sent at one time:

  • If you've received a notification that a limit has been met, you'll need to wait a set amount of time before you can send more emails. Most sending limit notifications inform you of how long you'll have to wait.
  • If you're planning to regularly send bulk email, consider looking into alternate solutions (like Yahoo! Groups, a Yahoo! Business account, or a third-party bulk email option).


(3) Additional Information

MailStore is investigating features to make archiving more seamless:

  • Support for logging into Yahoo mailboxes with OAuth2

Known issues in MailStore in relation to Yahoo:

  • There may be an unclear error message when connecting to Yahoo mailboxes when no unsafe apps are allowed, or when the user uses an invalid password. In this case, unsafe apps should be allowed (see the Yahoo article “Ways to securely access Yahoo Mail” on the website ( )
  • You may receive an incorrect error message when archiving a Yahoo mailbox stating that the IMAP server session has timed out. In general, the archiving process is completed. If this is not the case, archiving can be restarted.

Article-ID: KB20180131-0-EN (Deutsche Version)

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