March 2 (Reuters) - Apple Inc has blocked an update to email app BlueMail, which uses a customized version of OpenAI's GPT-3 language model, the co-founder of the app developer told Reuters on Thursday."Apple has blocked the BlueMail update and continues to treat BlueMail unfairly and to discriminate against us," Blix's Ben Volach said."Other GPT-powered apps seem not to be restricted," he added.Apple, which rejected the app update last week, asked the company to revise the app's age rating for those over 17 or implement content filtering, as BlueMail may produce content not appropriate for all audiences, according to a document viewed by Reuters."We want fair­ness. If we're re­quired to be 17-plus, then oth­ers should also have to," Volach tweeted, adding that many other apps that advertise ChatGPT-like features listed on Apple's app store do not have age restrictions.Apple, which was looking into the complaint, said developers have the option to challenge a rejection through the App Review Board process."It suggests to us that the company may scrutinize apps with ChatGPT functionality in the same way it does others where there are concerns about the quality of the user experience and appropriate nature of the content or service provided by the app," D.A. Davidson analyst Thomas Forte said.OpenAI's ChatGPT, which can generate content in response to user prompts, has captivated the tech industry.Microsoft and Alphabet Inc's Google both announced their own AI chatbots earlier in February.While AI-powered chatbots are a nascent field, early search results and conversations have made headlines with their unpredictability. (Reporting by Akash Sriram and Samrhitha Arunasalam in Bengaluru; Editing by Saumyadeb Chakrabarty, Maju Samuel and Krishna Chandra Eluri)