We need help with email deliverability issues

We are receiving errors when we send transactional Woo commerce emails and also some others. Here is an example:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

.....................@gmail.com
host gmail-smtp-in.l.google.com [172.253.62.26]
SMTP error from remote mail server after end of data:
550-5.7.26 This mail has been blocked because the sender is unauthenticated.
550-5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM.
550-5.7.26
550-5.7.26 Authentication results:
550-5.7.26 DKIM = did not pass
550-5.7.26 SPF [tefllessons.com] with ip: [185.201.16.53] = did not pass
550-5.7.26
550-5.7.26 For instructions on setting up authentication, go to
550 5.7.26 https://support.google.com/mail/answer/81126#authentication f3-20020a05620a408300b007872a3c1871si3922480qko.437 - gsmtp

Our email provider is A2 Hosting and our email is forwarded to gmail. We also use Cloudflare.

Our SPF and DKIM for our email server at A2 Hosting is configured correctly and authenticated, but the issue seems to be with the following IP (550-5.7.26 SPF [tefllessons.com] with ip: [185.201.16.53] = did not pass). when I look this up, it points to nl-spamexperts-1-mnt (Cogent Communications). We don't know who this company is or why our emails would be going through their mail server. See more info below:

% This is the RIPE Database query service.
% The objects are in RPSL format.
%
% The RIPE Database is subject to Terms and Conditions.
% See https://apps.db.ripe.net/docs/HTML-Terms-And-Conditions

% Note: this output has been filtered.
% To receive output for a database update, use the "-B" flag.

% Information related to '185.201.16.0 - 185.201.16.255'

% Abuse contact for '185.201.16.0 - 185.201.16.255' is 'abuse@spamexperts.com'

inetnum: 185.201.16.0 - 185.201.16.255
mnt-domains: nl-spamexperts-1-mnt
netname: NL-SPAMEXPERTS-EU-1
country: NL
admin-c: DVD265-RIPE
tech-c: DVD265-RIPE
status: LIR-PARTITIONED PA
mnt-by: nl-spamexperts-1-mnt
created: 2017-05-22T11:16:39Z
last-modified: 2017-06-27T11:59:20Z
source: RIPE

person: Dreas van Donselaar
address: Rokin 115
address: 1012KP
address: Amsterdam
address: NETHERLANDS
phone: +31208200004
nic-hdl: DVD265-RIPE
mnt-by: nl-spamexperts-1-mnt
created: 2017-04-26T13:05:23Z
last-modified: 2017-04-26T13:05:24Z
source: RIPE

% Information related to '185.201.16.0/24AS174'

route: 185.201.16.0/24
origin: AS174
mnt-by: nl-spamexperts-1-mnt
created: 2023-06-02T17:50:52Z
last-modified: 2023-06-02T17:50:52Z
source: RIPE

% This query was served by the RIPE Database Query Service version 1.109.1 (BUSA)

We are looking for someone who can determine why this mail server is sending emails on our behalf and to help us resolve the issue.