4.1 Conversation Limits

There is a limit of 50 conversations open at any one time.

4.2 File Transfer Limitations

If your attempts to upload attachments to a conference or to send files to a contact generate an error message, this means either that the contact that you’re sending the attachment to doesn’t have permission to receive files or that the file type is blocked. In Skype for Business Online, certain files types are blocked by the Intelligent Instant Message Filter (IIMF) application. IIMF helps protect Skype for Business Online users against the most common forms of viruses without degrading the user experience.

By default, Skype for Business Online is configured to prevent users from sending files through IM that have the following file name extensions:

.ade, .adp, .app, .asp, .bas, .bat, .cer, .chm, .cmd, .com, .cpl, .crt, .csh, .exe, .fxp, .grp, .hlp, .hta, .inf, .ins, .isp, .its, .js, .jse, .ksh, .lnk, .mad, .maf, .mag, .mam, .maq, .mar, .mas, .mat, .mau, .mav, .maw, .mda, .mdb, .mde, .mdt, .mdw, .mdz, .msc, .msi, .msp, .mst, .ocx, .ops, .pcd, .pif, .pl, .pnp, .prf, .prg, .pst, .reg, .scf, .scr, .sct, .shb, .shs, .tmp, .url, .vb, .vbe, .vbs, .vsd, .vsmacros, .vss, .vst, .vsw, .ws, .wsc, .wsf, .wsh

  • There are no file size limits for Peer-to-Peer communications
  • There is a 500MB file size limit for Meetings

Transferring files to Skype contacts isn't supported.

4.3 Meeting Limits across Office 365 options

  • File upload limit 
    The maximum size of files that can be uploaded to a Skype for Business meeting, including handouts and PowerPoint presentations is 500MB.
  • Participants in a Skype for Business meeting
    The maximum number of participants (including the presenter) who can join a single Skype for Business meeting is 250.
  • Presenters in a Skype for Business meeting 
    The maximum number of presenters in a single Skype for Business meeting is 250.
  • Skype for Business web app meeting participants
    The maximum number of Skype for Business web app meeting participants who can join a meeting is 250.
  • Skype for Business web app anonymous participants
    The maximum number of Skype for Business web app meeting participants who can anonymously join a meeting is 250.
  • Guests joining by phone
    The maximum number of guests who can call in to a meeting is 250.

4.4 Meeting Retention Limits

Customers using Skype for Business Online can upload content to a Skype for Business Meeting as attachments, such as PowerPoint presentations, OneNote files, and other files. The retention period for content that has been uploaded to a meeting is as follows:

  • One-time meeting
    Content is retained for 15 days starting from when the last person leaves the meeting.
  • Recurring meeting
    Content is retained for 15 days after the last person leaves the last session of the meeting. The retention timer resets if someone joins the same meeting session within 15 days. For example, assume a Skype for Business meeting is scheduled to occur on a weekly basis for one year, and a file is uploaded to the meeting during the first instance. If at least one person joins the meeting session every week, the file is retained in Skype for Business Online servers for the entire year plus 15 days after the last person leaves the last meeting of the series.
  • Meet Now meeting
    Content is retained for 8 hours after the meeting end time.

4.5 Meeting Expiration

Users can access a specific meeting after the meeting has ended, subject to the following expiration time periods:

  • One-time meeting
    Meeting expires 14 days after the scheduled meeting end time.
  • Recurring meeting with end date
    Meeting expires 14 days after the scheduled end time of the last meeting occurrence.
  • Meet Now meeting
    Meeting expires after 8 hours.

4.6 Summary Table of Limitations

FeatureLimit
File upload limit 500 MB
Participants in a Skype for Business meeting 250
Presenters in a Skype for Business meeting 250
Skype for Business web app meeting participants 250
Skype for Business web app anonymous participants 250
Guests joining by phone 250
Meeting content retention: One-time meeting

15 days

Meeting content retention: Recurring meeting 15 days
Meeting content retention: Meet Now meeting 8 hours
Meeting content retention: Meet Now meeting 8 hours
Meeting expiration: One-time meeting 14 days
Meeting expiration: Recurring meeting 14 days
Meeting expiration: Meet Now meeting 8 hours

4.7 Technical Notes

  • Users can add up to 250 contacts to their Skype for Business Contacts list.
  • Users each have a total of 200 concurrent presence subscriptions. Once that limit is reached, users can still send and receive instant messages and add users to a Contacts list, but they cannot see any additional presence information and will see a “Maximum Followers Reached” message when attempting to view a user's presence.
  • Distribution list expansion is allowed only for distribution lists with 100 or fewer individual members (regardless of the members’ presence or sign-in status).
  • Distribution lists with more than 100 members are allowed, but these distribution lists cannot be expanded to display individual list members.
  • A distribution list counts as one contact against the 250-contact limit per user, regardless of the number of individual members in the distribution list.
  • In Skype for Business, address book and Global Address List (GAL) lookups are performed through web requests only. The Skype for Business client doesn’t download and save a local copy of the address book. This reduces the load on the servers, and it provides the most up-to-date information possible when you perform a contact search.
  • The content-sharing feature is available for the Windows operating systems that are supported by Skype for Business.
  • Content sharing is subject to the network policies that the customer applies to its corporate, VPN, and wireless networks.
  • Content sharing is subject to the network policies that the customer applies to its corporate, VPN, and wireless networks.
  • The ability to share content and view shared content using Skype for Business varies depending on the client platform used.
  • Upload of other file types, including multimedia content, is not supported.
  • If you’re the presenter, you need to have PowerPoint installed on your computer in order to share a PowerPoint presentation in a Skype for Business meeting.

4.8 Ports and Outgoing Connections

PortProtocolDirectionUsage
443 STUN/TCP Outbound Audio, video, and application sharing sessions
443 PSOM/TLS Outbound Data sharing sessions
3478 STUN/UDP Outbound Audio and video sessions
5223 TCP Outbound Skype for Business mobile push notifications
50000-59999 RTP/UDP Outbound Audio and video sessions

Create a rule that allows outgoing connections (TLS and HTTPS) for all users to these locations:

  • *.partner.microsoftonline.cn
  • *.partner.microsoftonline-p.cn
  • *.onmschina.cn
  • *.sharepoint.cn
  • *partner.outlook.cn
  • *partner.lync.cn

Set the HTTP/SSL time-out value to eight hours.

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