There was a report earlier this year that IRS fax machine were not working because supplies could not be delivered to closed Service Centers and maintenance workers could not access the leased machines. However, there are more details in this April report from TIGTA, that suggests it might depend on which system IRS is using to receive your fax, on whether you should worry about its delivery:

“The IRS primarily relies on mail services and traditional fax services to receive correspondence from taxpayers. As of July 1, 2020, the IRS reported having 520 machines capable of receiving faxes in operation at its Tax Processing Centers. [Footnote: This includes 150 traditional fax machines and 370 multi-use copy machines.] During the time frame the Tax Processing Centers were closed, the IRS turned off fax machines to prevent correspondence from continuing to come in to the Tax Processing Centers while employees were not present to work the inventory.”

But in certain offices, IRS has the modern technology that allows it to receive faxes in the same way that I do:

“Expanded Electronic Fax (eFax) capabilities – This capability enables taxpayers to transmit documents to the IRS that would otherwise have to be mailed. For example, a taxpayer can fax documents and the IRS can then receive the documents without the need for a physical fax machine. Received faxes are electronically routed to an IRS e-mail inbox, with the fax content in a PDF attachment. The IRS was using eFax technology prior to the pandemic. However, in response to the pandemic, the IRS expanded the types of documents taxpayers can provide using eFax, as opposed to mailing to a Tax Processing Center. For example, the IRS allowed taxpayers to submit Form 1139, Corporation Application for Tentative Refund, and Form 1045, Application for Tentative Refund, through eFax. The IRS also established processes to allow businesses to use eFax to submit Form 7200 to claim the new COVID-related tax credits. Use of eFax allowed the IRS to receive these forms and assign them to be worked by employees who were teleworking.”

https://www.treasury.gov/tigta/auditreports/2021reports/202146029fr.pdf